feat(extraction): index Metal shader files (.metal) via the C++ grammar (#1121) (#1151)

.metal was absent from EXTENSION_MAP, so Metal Shading Language files were
silently skipped. MSL ≈ C++14, and the C++ grammar extracts its functions,
structs, type aliases, and call edges at parity with plain C++ — except MSL's
post-declarator [[attribute]] annotations, which misparse struct fields into
spurious extends refs from the struct to the field's own type (a wrong
inheritance edge whenever the repo typedefs float3/float4x4 itself, common in
shared ShaderTypes.h). blankMetalAttributes blanks them pre-parse,
offset-preserving, following the blankCppExportMacros pattern (#1061), gated
to .metal files only — in regular C++ the attribute position is legal syntax
the grammar parses natively. The preParse hook gains an optional filePath
param to support the gate.

Validated on llama.cpp's ggml-metal.metal (10.7k lines: 130 kernels vs 113
`kernel void` ground-truth lines, rope_yarn resolves its 4 kernel callers)
and SDL's shaders (PQtoLinear ← GetOutputColor), 0 bogus extends edges.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -13,6 +13,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 - The Claude Code context hook now recognizes prompts that describe code in plain words — in any language — by checking the prompt's words against the symbol names actually in your project's index. Asking about "the state machine des commandes" finds `OrderStateMachine` with no keyword involved. Confidence decides how much gets injected: structural questions and prompts naming a real symbol still get full context up front; a plain-words match gets a short pointer to the matching symbols so the agent queries them itself; everything else stays silent, exactly as before.
 - Anonymous usage telemetry now counts how often the context hook injected context, offered a hint, or stayed silent — fixed counter names only; the prompt's content is never stored or sent. This makes the hook's accuracy measurable instead of guessed. The counters record what actually happened, not what was attempted: a lookup that errors or comes back empty counts as a distinct silent outcome, never as delivered context (#1143, thanks @inth3shadows).
+- Metal shader files (`.metal`) are now indexed. Metal Shading Language is close enough to C++ that vertex/fragment/kernel functions, structs, type aliases, and the calls between them all land in the graph — so shader pipelines in Apple-platform projects show up in impact analysis and flow traces instead of being silently skipped. Metal's `[[buffer(0)]]`-style attribute annotations are handled so they can't corrupt what gets extracted. Thanks @FluxKo for the report. (#1121)
 
 ### Fixes