fix(parsers): allow asset names beginning with two dots

[javierivanov]

What

Fix local asset resolution and containment checks for valid names beginning with two dots, such as ..intro.mp4 and ..assets/clip.mp4.

Why

The checks treated every relative path starting with .. as traversal. As a result, local assets with these names were rejected even when they were inside the project. The candidate resolver returned no candidates, which can produce false missing-asset reports.

How

Check for the complete parent-directory segment (.. or .. followed by the platform separator). Apply the same distinction to the existing POSIX-normalized root-clamping fallback. Actual parent and sibling paths remain outside the containment boundary.

Test plan

• Added 8 regression cases covering dot-prefixed files/directories, parent/sibling rejection, root equality, and root-clamping behavior. Four cases failed before the fix.
• All 30 focused tests passed: bun run --cwd packages/parsers test --configLoader runner src/assetPaths.test.ts src/assetResolution.test.ts src/rewriteSubCompPaths.test.ts.
• Parser typecheck passed: bun run --cwd packages/parsers typecheck.
• oxlint, oxfmt, fallow audit, tracked-artifact, large-file, and commit-message checks passed.
• Full monorepo build passed: bun run build.
• The broader pre-commit typecheck commands passed after generating build artifacts: core, studio, and scripts TypeScript checks.
• Full parser suite after building: 935 passed, 2 failed, 4 skipped, 3 todo. Both failures are existing ffBinaries.test.ts Windows failures, reproduced against the original code (Windows exe preference and PATH fallback spy count).