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/tests/db_schema_golden.rs

@@ -172,6 +172,15 @@ fn db_schema_matches_expected_columns() {
             ("name", "VARCHAR"),
             ("kind", "VARCHAR"),
         ]),
+        ("demangled_names", &[
+            ("address", "BIGINT"),
+            ("mangled", "VARCHAR"),
+            ("raw_demangled", "VARCHAR"),
+            ("namespace_path", "VARCHAR"),
+            ("class_name", "VARCHAR"),
+            ("method_name", "VARCHAR"),
+            ("params_signature", "VARCHAR"),
+        ]),
         ("xrefs", &[
             ("source", "BIGINT"),
             ("target", "BIGINT"),