fix(code-nav): stop excluding source packages named vendor, target, build, dist or coverage (#1559)

* fix(code-nav): stop excluding source packages named vendor/target/build (#1558)

A ripgrep glob with no slash matches a path segment at any depth, so
--glob !vendor pruned first-party Java packages such as
src/main/java/com/example/vendor/app/ and code navigation reported
'No results'.

Split the exclusion list: names that can only be tool output stay
excluded at any depth, while the ambiguous names (vendor, target,
build, dist, coverage) are now excluded only at the search root via an
anchored glob. Nested copies that really are build output are already
skipped by ripgrep's default .gitignore handling.

Belt and braces: a segment the request's own file lives under is never
excluded for that request, so a symbol in a changed file can always
find its siblings.

* test(code-nav): cover the #1558 exclusion split

Unit tests for the anchored/unanchored glob split and the origin-file
rule, plus real-ripgrep coverage over a temp fixture (skipped cleanly
when rg is not on PATH).