fix(drift): treat qualified-name symbol notation as not a path

[dyk1454683243-sudo]

What

Treat symbol / qualified-name notation such as `src/auth/login.validateToken` as not a filesystem path, so it never becomes a path claim or MISSING_PATH.

isNotAPath now rejects values whose final slash-segment matches identifier.identifier (JS/TS method or property) and does not end in a known file extension. Real files stay claims: src/auth/login.ts, .mex/ROUTER.md, package.json. Extra dotted segments such as foo.d.ts are left for #216.

Why

Addresses #202 (bullet 1 only).

Do not treat this as Fixes #202 or Closes #202 — that would auto-close the whole mega-issue.

Remaining #202 bullets stay open:

2. Compound extensions (.d.ts) — owned by fix(drift): treat compound extensions like .d.ts as not-paths #216
3. Hypothetical examples (./x, x.ts, x/index.ts)
4. Alternation shorthand (tests/grounding|traversal|…)
5. Scoped-package resolve (@scope/pkg/package.json vs bare specifier) — owned by fix(drift): resolve scoped packages by bare specifier #217
6. gitignore trailing-slash directory exemption — owned by fix(drift): honor trailing-slash gitignore rules for absent paths #218

Type of change

• Bug fix
• New feature
• Refactor
• Docs
• CI/Tooling

How to test

1. npx vitest run src/drift
2. Confirm markdown that cites `src/auth/login.validateToken` as a qualified_name example produces zero path claims and zero MISSING_PATH.
3. Confirm a real missing file such as src/auth/login.ts is still reported as MISSING_PATH.
4. Confirm existing MISSING_PATH false positives: negation only heading-scoped, non-path tokens treated as paths, dot-dir glob blind spot #143 cases stay green, and .mex/ROUTER.md / package.json still extract as path claims.
5. npm run typecheck

Checklist

• Focused drift tests pass (npx vitest run src/drift — 12 passed, 1 skipped #201 version-shaped case left untouched)
• Claims extraction tests pass (npx vitest run test/claims.test.ts — 30 passed, including the bullet-1 skip plus preserved real paths)
• Typecheck passes (npm run typecheck)
• Tests pass (npm test) — full suite is not the gate for this isNotAPath filter
• No breaking changes (or documented below)
• Tested locally with a real project

Code-graph changes

• This PR targets main
• A linked issue agrees on the bounded extractor/resolver scope
• The change follows the frozen LanguageExtractor or FrameworkResolver interface
• A focused fixture and assertions for the expected node/edge shape are included
• Any new grammar WASM, extension mapping, extractor, or resolver is registered
• No graph identity, reconciliation, schema, or drift-semantics changes are included, or a core / discuss-first issue is linked above

This is a drift claim-extraction filter only. It does not change graph identity, extractors, or the other #202 bullets. Issue #202 stays open.