chore: add migration/ bundle for cross-machine setup

Bundles state that lives OUTSIDE the xenia-rs repo so a fresh clone on
another machine can be brought up to identical configuration via
migration/setup.sh:

  - claude-memory/             ~/.claude/projects/-home-fabi-RE-Project-Sylpheed/memory/
                               (103 files, 1.1 MB - MEMORY.md + every
                                project_xenia_rs_*.md from audits
                                addis_signext through audit-058)
  - project-root/dot-claude/   <project-root>/.claude/settings.json
                               (Stop hook + permissions)
  - project-root/ppc-manual/   <project-root>/ppc-manual/
                               (PowerPC reference docs, 397 files, 3.7 MB)
  - project-root/run-canary.sh <project-root>/run-canary.sh
  - README.md                  Human-readable setup checklist
  - setup.sh                   Idempotent installer (also reclones
                               xenia-canary at pinned HEAD 6de80dffe)
  - MANIFEST.md                Per-file mapping + per-file-not-bundled
                               restoration recipe

Excluded from bundle (not shippable via git):
  - Sylpheed ISO (7.8 GB; copyright; manual copy required)
  - sylpheed.db (395 MB; regenerable from XEX via analysis tooling)
  - target/ build artifacts (rebuild on target)
  - audit-runs probe firehoses (.log/.stdout/.stderr ~11 GB; rerun if needed)
  - audit-runs memory dumps (.bin ~4.5 GB; rerun audit-026/027/029 if needed)
  - xenia-canary checkout (setup.sh reclones from
    git.mc02.dev/fabi/Xenia-Canary.git at HEAD 6de80dffe)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

migration/project-root/ppc-manual/forms/XFX.md

@@ -0,0 +1,24 @@
+# Form `XFX` — XFX — Fixed (SPR/TBR/CR-field access)
+
+## Bit Layout
+
+| Bits | Field | Meaning |
+| --- | --- | --- |
+| 0–5 | `OPCD` | primary opcode (31) |
+| 6–10 | `RT` | destination / source GPR |
+| 11–20 | `spr/tbr/FXM` | SPR/TBR number (byte-swapped halves) or CR field mask |
+| 21–30 | `XO` | extended opcode |
+| 31 | `—` | reserved |
+
+## Instructions Using This Form
+
+<!-- GENERATED: BEGIN -->
+
+| Mnemonic | Opcode | Group | Description |
+| --- | --- | --- | --- |
+| [`mtcrf`](../control/mtcrf.md) | `0x7c000120` | control | Move to Condition Register Fields |
+| [`mfspr`](../control/mfspr.md) | `0x7c0002a6` | control | Move from Special-Purpose Register |
+| [`mftb`](../control/mftb.md) | `0x7c0002e6` | control | Move from Time Base |
+| [`mtspr`](../control/mtspr.md) | `0x7c0003a6` | control | Move to Special-Purpose Register |
+
+<!-- GENERATED: END -->