docs: define the status markers, and fix six mislabelled or superseded entries

An audit of BACKLOG.md turned up a class of error with a single root cause: the
README defines only the CONFIRMED/PROBABLE/HYPOTHESIS confidence scale, while
the pages actually use a second vocabulary -- and 🔴 appears 98 times without
ever being defined.  It gets used for two different things, "refuted" and
"blocked", and three entries slid from one into the other.

README now defines ✅/🟡/❔/🔴/❌/🚧 and states the rule the corpus was missing:
🔴 never means "we have not run it yet".  That is ❔ or 🚧.  Its blocked sense is
only for a real limit of the box -- no push credentials, no hardware Vulkan, a
decision only the user can make -- and since the box can run the emulator,
script input, screenshot and read guest memory, "needs a run" is never blocked.
I made exactly this mistake on the world-unit item earlier today, which is what
prompted looking for others.

Fixed in BACKLOG.md:

  * the elimination test, marked 🔴 UNRUN and in fact run and refuted nine
    lines further down;
  * the frozen capture, marked 🔴 STILL UNRUN and in fact taken eleven lines
    down -- 🔴 wrong twice, since "the freeze did not happen this run" is a
    scheduling outcome and not a refutation;
  * a 🚧 STILL UNRUN item whose stated blocker (the boot-nav bug) is fixed;
  * the objective-counter heading, which asserts 0xbdb59668 as the answer while
    its own first body line refutes that address -- retitled to say what is
    actually solved, the method;
  * the paint-order "third measured permutation" question, answered inside its
    own entry by a third, fourth and fifth screen;
  * the UTF-16 endianness question -- resolved, and it is not a stale comment:
    localization.rs both documents LE and decodes with u16::from_le_bytes, so
    it is a code bug worth filing.

Also fixes the corpus's only dangling link (INDEX.md pointed at
structures/idxd-unnamed-keys.md, never written).

docs/re/INDEX.md

@@ -12,7 +12,7 @@ Promote to a prose `structures/…md` file when a format needs behavioural notes
 |--------|-------|-----------------------|-------|
 | IPFB `.pak` archive | ✅ | `sylpheed-formats/src/pak.rs` + `tests/pak_idxd_disc.rs` | header + 12-byte TOC, Z1/zlib payloads |
 | name-hash (TOC keys) | ✅ | `sylpheed-formats/src/hash.rs` | Barrett-reduction hash; recovers original paths |
-| IDXD object/table | ✅ | `sylpheed-formats/src/idxd.rs` + `tests/idxd_records_disc.rs` ([container](structures/idxd-container.md)) | **The binary record/index region in front of the string pool is DECODED** (2026-08-25), closing the parser's long-standing "not yet decoded" note. Uniform 16-byte records `{name_hash, name_off, field_begin, field_end}` sorted by hash and binary-searched, then a field count, 12-byte fields `{key, name_off, value_off}` sorted by key, a pool size, and the string pool; the trailing `pool_size == file_len - pool_base` identity makes the layout self-checking. Verified over the **whole disc** with **zero** failures: 7 750/7 750 objects, 190 782/190 782 records reproducing their stored `tag_hash`, 1 271 462/1 271 462 named fields reproducing their key — and `IXUD` is the same container with `ixud_hash`, UTF-16BE and all offsets in **chars** (1 104/1 104 objects, 628 165/628 165 fields). **Field names are stored on disc** — a field's middle word points at its own name — so nothing needs preimage search except the **504** field entries disc-wide that are hash-keyed with no name — which are only **42 distinct keys**, each in 12 places (see [idxd-unnamed-keys.md](structures/idxd-unnamed-keys.md)), and are provably unrecoverable from the hash alone; the other 1 485 073 nameless fields are *positional*, keyed by a literal integer (line slots, movie ids). ⚠️ **Two long-held beliefs WITHDRAWN**: the word at `0x08` is **not a schema hash**, it is record 0's `name_hash` (7 750/7 750) — the header has no type field at all, so an object's kind is known only from the caller that loads it; and the field's middle word is **not** an always-`0xFFFFFFFF` flags word. The first was caught by a test asserting that every movie id names a real record: `1005 -> STAGE10_PHASE01` failed because `tag_hash("STAGE10_PHASE01")` **is** `0x067025B9`, that table's supposed schema id. 🟡 the legacy value-before-key string-pool reader is now known to be an *approximation* of the real table, and every number derived from it is re-checkable but not yet re-checked |
+| IDXD object/table | ✅ | `sylpheed-formats/src/idxd.rs` + `tests/idxd_records_disc.rs` ([container](structures/idxd-container.md)) | **The binary record/index region in front of the string pool is DECODED** (2026-08-25), closing the parser's long-standing "not yet decoded" note. Uniform 16-byte records `{name_hash, name_off, field_begin, field_end}` sorted by hash and binary-searched, then a field count, 12-byte fields `{key, name_off, value_off}` sorted by key, a pool size, and the string pool; the trailing `pool_size == file_len - pool_base` identity makes the layout self-checking. Verified over the **whole disc** with **zero** failures: 7 750/7 750 objects, 190 782/190 782 records reproducing their stored `tag_hash`, 1 271 462/1 271 462 named fields reproducing their key — and `IXUD` is the same container with `ixud_hash`, UTF-16BE and all offsets in **chars** (1 104/1 104 objects, 628 165/628 165 fields). **Field names are stored on disc** — a field's middle word points at its own name — so nothing needs preimage search except the **504** field entries disc-wide that are hash-keyed with no name — which are only **42 distinct keys**, each in 12 places (the page for these was never written — the finding is in this row), and are provably unrecoverable from the hash alone; the other 1 485 073 nameless fields are *positional*, keyed by a literal integer (line slots, movie ids). ⚠️ **Two long-held beliefs WITHDRAWN**: the word at `0x08` is **not a schema hash**, it is record 0's `name_hash` (7 750/7 750) — the header has no type field at all, so an object's kind is known only from the caller that loads it; and the field's middle word is **not** an always-`0xFFFFFFFF` flags word. The first was caught by a test asserting that every movie id names a real record: `1005 -> STAGE10_PHASE01` failed because `tag_hash("STAGE10_PHASE01")` **is** `0x067025B9`, that table's supposed schema id. 🟡 the legacy value-before-key string-pool reader is now known to be an *approximation* of the real table, and every number derived from it is re-checkable but not yet re-checked |
 | XPR2 texture + cubemap | 🟡/✅ | `sylpheed-formats/src/texture.rs` + [colour check](xpr2-colour-check.md) | de-tile + A8R8G8B8 and DXT1. **Channel order ✅ confirmed against the running game**: the Delta Saber's decoded atlas is orange-dominant (median saturated hue 23.3°, *zero* cool pixels) and the game renders the same hull at 9.3° — a red↔blue swap would sit at ≈200°. Exact fidelity (gamma/sRGB curve, premultiplied alpha, per-channel scale) is 🟡 untested, since a hue comparison cannot see it; cubemap face ordering ❔ |
 | T8aD 2D texture | ✅ | `sylpheed-formats/src/t8ad.rs` | **100 % of the disc decodes** (19 216/19 216, measured). The "~15 % deferred variants" were a wrong model, not a variant: a surface is a list of **arbitrary sub-rectangles**, each with a 16-byte header of `dst X, dst Y, width, height`, not a 256×256 grid — `0x1c` is the **rectangle count**. Uncovered area stays transparent. **Colours ✅ CONFIRMED** ([k8888](structures/texture-color-k8888.md)) |
 | RATC bundle | ✅ | `sylpheed-formats/src/ratc.rs` | child listing confirmed. **"One level deep" is not a limitation — there is nothing deeper**: 2 859 bundles hold 18 002 children at depth 1 and **0 at depth 2**, with no parse failures. Nested RATC blobs are **leaf records that reference siblings by name** (`opt `, the sprite name): 3 311 leaves, all embedding sibling names, **10 144 of 10 148 references resolve**. The 4 that do not are one dangling asset — `pmbase.rat` → `pmbase.t32` in `GP_STAGE_CLEAR.pak`'s four language builds, and `pmbase.t32` is **on the disc nowhere** |