feat(incremental): ignore AWS CDK synth output

[tirth8205]

What changed

• Ignore AWS CDK cdk.out synth artifacts at the repository root and inside monorepo packages.
• Add regression coverage for root, nested, and similarly named non-artifact directories.
• Keep *.bundle.js out of the built-in defaults because users cannot negate a default ignore pattern.

Why

This ports only the safe, current-main-compatible part of Gideon Zenz's PR #335 (commit 448e48c). CDK synth output is generated code that should not pollute the graph, while a global bundle-file default would be irreversible for repositories that intentionally track those files.

Gideon Zenz is preserved as co-author on the commit.

Validation

• TDD red: the new CDK regression failed on current main because cdk.out/manifest.json was not ignored.
• Focused ignore suite: 9 passed.
• Full suite after rebase: 1489 passed, 2 xpassed.
• CI lint scope: ruff check code_review_graph/ passed.
• Changed-file lint and git diff --check passed.
• Knowledge-graph review found no affected execution flows; the change is limited to the default ignore constant and its regression test.

[github-actions]

code-review-graph review

Overall risk: 0.25 (LOW) — 2 changed function(s)/class(es), 0 affected flow(s), 1 test gap(s)

Risk-scored changes

Risk	Level	Symbol	Location	Tested
0.25	low	tests/test_incremental.py::TestIgnorePatterns.test_cdk_output_default_matches_at_any_depth	tests/test_incremental.py:271	(test)
0.20	low	tests/test_incremental.py::TestIgnorePatterns	tests/test_incremental.py:188	no

Test gaps

• tests/test_incremental.py::TestIgnorePatterns (tests/test_incremental.py:188)

Token savings: this graph-backed report used ~20,075 fewer tokens (~97%) than reading every changed file in full (estimated, chars/4 approximation).

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