fix: route configured null-language extensions to line-count instead of skipped-unsupported (#1274)

[alpurkan17]

Summary

Extensions in programming_languages.json with language=null (no tree-sitter parser) receive score=0.0 with scoring_method=skipped-unsupported. The scorer only routed to line-count when the extension appeared in NON_CODE_EXTENSIONS — it never consulted the JSON config for null-language entries.

This affects 11 extensions: env, gitattributes, gitignore, gql, graphql, ipynb, move, nim, pde, puml, tex.

Fix: add an inline check before the skipped-unsupported gate: when the extension is configured in programming_languages with language=null, route to line-count scoring using the configured weight. No new method, no import changes — single inline check in the existing elif chain.

Validation

• uv run ruff check — clean
• uv run ruff format --check — clean
• uv run pyright — 0 errors / 0 warnings
• uv run pytest tests/ -k "null_language or line_count" -q — 30/30 passed

Closes #1274

[anderdc]

Duplicate of #1275 which is better scoped/implemented. Closing.