fix(parse): zig symbol anchors never resolved — query targeted wrong grammar node names

[laulauland]

Problem

Symbol-level anchors on .zig files (drift link doc.md src/file.zig#Symbol) have never worked — every attempt fails with cannot compute fingerprint. The repo's own drift.lock contains zero #Symbol bindings, which is how this went unnoticed.

Root cause: src/queries/zig.scm targets maxxnino-style node names (TopLevelDecl, FnDecl, VarDecl, IDENTIFIER), but the grammar we build against is tree-sitter-grammars/tree-sitter-zig v1.1.1, which uses function_declaration, variable_declaration, identifier. The query never compiled — and fingerprintSymbolSyntax swallows ts.Query.create failures into null (symbols.zig), so the compile error surfaced as a generic fingerprint failure.

Fix

• Rewrite src/queries/zig.scm for the actual grammar. variable_declaration has no name: field, so the pattern anchors the first named child (. (identifier) @name) to avoid matching initializer identifiers on the RHS.
• Error message now names the failing target instead of the doc: error: cannot compute fingerprint for target: src/vcs.zig#noSuchSymbol (was: ...for anchor in '<doc-path>'). Contextual printing moved into link.zig next to the existing TargetNotFound/HeadingNotFound messages, covering both targeted and blanket relink paths.

Tests

• symbol queries compile for every supported language — compiles all six .scm queries against their linked grammars; would have caught this bug and protects every future grammar bump.
• zig fn/const symbol resolution, missing-symbol returns null, initializer identifiers don't false-positive.
• Dogfood: drift.lock gains docs/DESIGN.md -> src/vcs.zig#getRepoIdentity and #GitCatFile — the first symbol-level zig bindings in the repo, both genuinely described in DESIGN.md. Stale-doc relinks for the code edits reviewed per the drift skill (prose unaffected).

Fixes DRIFT-ezbuwwor.