[M3] mxaccess-galaxy: GalaxyTagMetadata + parser + Resolver trait + SQL

Lands M3 stream A — the pure-Rust foundation of the Galaxy resolver:
the data type, the tag-reference parser, the async trait, and the
canonical SQL strings. Unblocks F13 (NmxClient::write_* wrappers depend
on GalaxyTagMetadata) without pulling in tiberius yet.

New
- metadata.rs (~195 LoC, 7 tests) — GalaxyTagMetadata record (port of
  cs:6-73). Includes is_buffer_property + to_reference_handle(galaxy_id)
  bridging into mxaccess-codec::MxReferenceHandle::from_names.
- parser.rs (~330 LoC, 12 tests) — ParsedTagReference parser. Handles
  Object.Attribute (1 candidate), Object.Primitive.Attribute (2
  candidates: primitive-attr first, dotted-attr second per cs:181-185),
  and the case-insensitive .property(buffer) suffix. Pure-Rust, no I/O.
- resolver.rs (~200 LoC, 5 tests including a tokio-driven InMemoryResolver
  proving the trait is implementable without SQL) — async Resolver trait
  + ResolverError. Default browse returns Backend("not implemented") so
  read-only backends don't need to override it.
- sql.rs (~280 LoC, 5 smoke tests) — RESOLVE_SQL + BROWSE_SQL constants
  ported byte-for-byte from cs:208-432. Available publicly so any
  backend (the planned tiberius impl, a wwtools/grdb snapshot replay,
  etc.) can grab the canonical query.

Cargo.toml: added mxaccess-codec (path), async-trait, thiserror;
tokio added as dev-dependency for the resolver-trait async tests.

Deliberately deferred to a later iteration:
- The tiberius-backed Resolver impl behind the galaxy-resolver feature.
- ToValueKind / TryGetValueKind / ProjectWriteValue helpers on
  GalaxyTagMetadata (cs:41-72) — these need a MxDataType -> MxValueKind
  lookup that the codec doesn't currently expose; landing them with
  F13's write-helper iteration keeps the iteration coherent.

Test count delta: 397 -> 427 (+30). All four DoD gates green.
Open followups touched: F13 prerequisite (GalaxyTagMetadata) now in
place; F13 itself stays open until the write helpers wire it up.

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

rust/Cargo.lock

@@ -2,6 +2,17 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "async-trait"
+version = "0.1.89"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9035ad2d096bed7955a320ee7e2230574d28fd3c3a0f186cbea1ff3c7eed5dbb"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "block-buffer"
 version = "0.10.4"
@@ -205,6 +216,12 @@ dependencies = [
 [[package]]
 name = "mxaccess-galaxy"
 version = "0.0.0"
+dependencies = [
+ "async-trait",
+ "mxaccess-codec",
+ "thiserror",
+ "tokio",
+]
 
 [[package]]
 name = "mxaccess-nmx"