fix(extract): filter Kotlin builtin/stdlib types from references graph

[kebwlmbhee]

Problem

_java_collect_type_refs filters out JDK builtin types via _JAVA_BUILTIN_TYPES before emitting a graph node/edge, and the same pattern exists for Python (_PYTHON_ANNOTATION_NOISE) and Go (_GO_PREDECLARED_TYPES). _kotlin_collect_type_refs has no equivalent — every Boolean, String, Int, List, ... language-level type annotation in a .kt file becomes a real graph node/edge.

In practice this means two unrelated Kotlin files that share nothing but Boolean/String/Int type annotations get treated as connected, and cluster-only groups them into the same community — a false positive with no real code coupling behind it. Confirmed by checking actual import statements between files in a real project: zero relation beyond one legitimate case.

Fix

Add _KOTLIN_BUILTIN_TYPES mirroring _JAVA_BUILTIN_TYPES (kotlin.* scalars, collections, and throwables — deliberately not Android/JVM framework types like Context/View/Bundle, staying consistent with how _JAVA_BUILTIN_TYPES doesn't filter framework-specific types either), and check it plus _JAVA_BUILTIN_TYPES (Kotlin freely references java.util.Date/UUID/etc) at the three call sites in _kotlin_collect_type_refs that previously appended unconditionally.

Deliberately excludes "Result" from the filter even though kotlin.Result exists — it collides with the very common user-defined sealed-class name. Confirmed against this repo's own tests/fixtures/sample.kt, which defines its own class Result<T>; an earlier version of this patch that included "Result" broke test_kotlin_parameter_return_generic_and_field_contexts.

Evidence

Real-world Android/Kotlin project (~400 source files), full graphify . --code-only + cluster-only . --no-label:

	Before	After
Nodes	3693	3239 (-12%)
Edges	6481	5221 (-19%)
Communities	269	271

Concretely: a utility file (ScreenExt.kt, purely Int/Float typed screen-dimension helpers) went from being merged into a 5-file grab-bag community (connected only via shared Boolean/Int type nodes) to splitting cleanly into its own community.

Testing

• Added test_kotlin_builtin_types_not_emitted_as_references and test_kotlin_user_types_still_emit_references to tests/test_languages.py (the latter guards specifically against the Result collision above).
• Full suite: 3142 passed, 31 skipped — the 5 failures on a clean checkout of v8 (test_collect_files_skips_hidden, 4x test_ollama_retry_cap.py needing the optional openai package) are pre-existing/environmental and unaffected by this change (verified by running the same tests against v8 with this commit stashed out).

Scope note

This intentionally does not touch Android/JVM framework types (Context, View, Bundle, SharedPreferences, JSONObject, ...). Those still create some false-hub clustering in Android projects specifically; filtering them is a separate, more debatable scope-expansion (you'd lose "who touches SharedPreferences" as a real signal) and isn't part of this PR.