M2: MSVC C++ demangler + demangled_names DB table

Adds an MSVC name-demangling layer in front of M3's vtable / RTTI work:
- New `xenia_analysis::demangle` wraps the `msvc-demangler` crate (a Rust
  port of LLVM's `MicrosoftDemangle.cpp`). `demangle()` short-circuits on
  non-mangled inputs (`?` prefix check); `demangle_or_raw()` always returns
  a record (raw passthrough on parse failure).
- Heuristic split of the formatted demangled string into structured fields
  `(namespace_path, class_name, method_name, params_signature)`. Top-level
  paren / template-bracket aware, so `a::b<c::d>::e` and signatures with
  templated arg types parse correctly.
- DB: new `demangled_names(address, mangled, raw_demangled, namespace_path,
  class_name, method_name, params_signature)` with indices on address /
  class_name / method_name. Populated from any label whose name starts with
  `?` plus any import name that happens to be mangled.

For Sylpheed (a fully stripped binary) this table is empty out-of-the-box;
the layer's value lands in M3, which will append rows for every RTTI
TypeDescriptor name found in `.rdata`.

Tests 610→617 (+7 demangler unit tests covering early-out, raw fallback,
member function form, RTTI form, qname split, paren-template safety, and
top-level `::` splitting).

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

crates/xenia-analysis/SCHEMA.md

@@ -71,13 +71,36 @@ SELECT name FROM functions WHERE address = 2186674160;  -- 0x824D29F0
 
 ---
 
-## Layer M2 — MSVC C++ name demangler (planned)
+## Layer M2 — MSVC C++ name demangler (landed)
 
-Adds `demangled_names(address, mangled, namespace_path, class_name,
-method_name, params_signature, raw_demangled)`. Populates from any label /
-import / RTTI string starting with `?`. Falls back to `raw_demangled = mangled`
-when the parser cannot decode (e.g. exotic templates). See
-`crates/xenia-analysis/src/demangle.rs` (when landed).
+### Schema additions
+- New table `demangled_names(address BIGINT NULL, mangled VARCHAR NOT NULL,
+  raw_demangled VARCHAR NOT NULL, namespace_path VARCHAR NULL,
+  class_name VARCHAR NULL, method_name VARCHAR NULL,
+  params_signature VARCHAR NULL)`.
+- Indices on `address`, `class_name`, `method_name`.
+
+### What this layer does
+- Wraps `msvc_demangler::demangle` (a Rust port of LLVM's
+  `MicrosoftDemangle.cpp`) and splits the formatted output into structured
+  fields via a heuristic top-level parser (handles templates and nested parens
+  correctly).
+- Populates `demangled_names` from any label whose name starts with `?` plus
+  any import name that happens to be mangled (defensive — typical kernel
+  imports use C names).
+
+### What this layer does NOT do
+- Does not parse the AST returned by `msvc_demangler::parse` — uses the formatted
+  string and a heuristic split. Adequate for typical class member functions
+  and RTTI strings; exotic template / lambda forms still get `raw_demangled`
+  populated but may have NULL structured fields.
+- Does not yet ingest RTTI strings discovered in `.rdata` — that's M3's job;
+  M3 will append rows to this table at the addresses where it finds RTTI
+  TypeDescriptors.
+
+### Reference docs
+- `msvc-demangler` crate (`https://docs.rs/msvc-demangler/0.11`).
+- LLVM `MicrosoftDemangle.cpp` (the parser this crate ports).
 
 ## Layer M3 — Vtable + RTTI detection (planned)