fix(indexing): canonicalize vendor scan paths

[sidux]

Summary

• retain both configured and canonical spellings of vendor directories
• classify classes reached through filesystem aliases as dependency code
• purge stale vendor functions and constants through either path spelling during Composer rescans
• cover aliased vendor registration, rescans, and origin classification with Unix regression tests

Why

Workspace walkers and Composer discovery can observe the same directory through different filesystem spellings, especially where the operating system exposes path aliases. Comparing only the configured spelling makes dependency files look like project files, so indexing can enter the vendor tree, do far more work than expected, and distort completion ranking. Normalizing both forms keeps the exclusion and provenance rules consistent.

Validation

• 3 focused vendor-path alias tests passed
• cargo clippy --fix --allow-dirty -- -D warnings
• cargo fmt
• cargo clippy --all-targets -- -D warnings
• cargo test — 14,102 passed, 12 ignored

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/indexing/scan.rs	80.00%	1 Missing ⚠️

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