fix: replace substring pattern matching with globset in FileWalker

[oudeis01]

Problem

matches_patterns() used path_str.contains(pattern) to check include and exclude patterns. This treats every pattern as a literal substring, so glob-style inputs like **/vendor/** or **/*.rs never match any real path -- the string "**/vendor/**" is simply not a substring of "project/vendor/foo.c".

The globset crate is already a declared dependency in Cargo.toml but was unused in this module.

Fix

• Add build_glob_set() to compile patterns into a GlobSet once in with_patterns(), avoiding recompilation on every call to matches_patterns().
• Rewrite matches_patterns() to match against the path relative to the walk root, so patterns behave correctly regardless of where the root directory sits in the filesystem.
• Update tests to use proper glob patterns (**/*.rs, **/target/**, etc.) that reflect real-world usage.

Test plan

• cargo test --lib indexer::file_walker passes (34 tests)
• Indexing with exclude_patterns: ["**/vendor/**"] correctly skips vendored files
• Indexing with include_patterns: ["**/*.rs"] correctly includes only Rust files

[Waxolunist]

Please merge. Include and exclude patterns don't work currently