fix(tsconfig): resolve non-relative imports against baseUrl

[Balghisa12]

Pull Request

Linked issue

No existing issue. Found while evaluating the graph on a NestJS monorepo. Related to #1030 (workspace packages), which is a separate gap.

What & why

TsconfigResolver.resolve_alias returned None whenever compilerOptions.paths was empty, so a tsconfig that sets only baseUrl resolved no non-relative import. tsc resolves such specifiers against baseUrl, both without paths and when no paths pattern matches. The resolver now does the same, after trying paths. docs/FEATURES.md already lists paths/baseUrl resolution, so no docs change.

On a NestJS service of 1,181 TypeScript files that imports src/... with "baseUrl": "./" and no paths:

• unresolved src/... import edges: 1,849 → 44 (the 44 point at generated clients absent from the checkout);
• the import edges are identical to declaring "paths": { "src/*": ["src/*"] }, which takes importers_of for one service from 14 to 35 of its 35 importers and the real callers callers_of finds for its method from 4 to all 6.

How it was tested

uv run pytest tests/test_tsconfig_resolver.py -q   # on staging: 2 failed (the two baseUrl cases); with the fix: 15 passed
uv run pytest tests/ --tb=short -q                 # 4272 passed, 850 skipped, 2 xfailed, 2 xpassed
uv run --extra dev ruff check code_review_graph/   # All checks passed
uv run --extra dev mypy code_review_graph/ --ignore-missing-imports --no-strict-optional  # no issues in 77 files
uvx bandit -q -r code_review_graph/tsconfig_resolver.py -c pyproject.toml                # clean

tsc 5.8.3 with --traceResolution on two fixtures, baseUrl alone and baseUrl with a non-matching paths entry, resolves src/lib/util through baseUrl in both.

Checklist

• Tests added for new functionality
• All tests pass: uv run pytest tests/ --tb=short -q
• Linting passes: uv run ruff check code_review_graph/
• Type checking passes: uv run mypy code_review_graph/ --ignore-missing-imports --no-strict-optional
• Lines are at most 100 characters
• Docs updated where behavior changed (README, docs/, docstrings)

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