Vendor generated fixtures/notebooks; fix .github over-vendoring vs CI detection

[nielsbosma]

Implements two reviewed suggestions (data-only changes in data/vendor.yml).

1. Vendor generated fixtures / notebooks (vendor-add-generated-fixture-patterns.md)

Large generated/recorded files were counted at full byte weight. Added vendor patterns:

• (^|/).*\.ipynb$ — Jupyter notebooks (type=markup, so the prose/data language filter does NOT drop them; this is the only thing that excludes their base64 output cells which inflate byte share ~1000x).
• (^|/)cassettes/ and (^|/)[Tt]ests?/cassettes/ — VCR.py / betamax recorded HTTP fixtures.
• (^|/)NOTICES\.txt$ and (^|/)THIRD[-_]PARTY[-_ ]?NOTICES(\.[A-Za-z]+)?$ — generated third-party notices.
• (^|/)memory-tests/ and (^|/)perf-tests/ — large generated test-session fixtures.

2. Fix .github/ over-vendoring vs CI detection (github-dir-over-vendored-kills-ci-detection.md)

Vendoring the entire .github/ tree made FileSystemScanner prune the whole directory during the walk, so .github/workflows/ files never reached InfraScanner — the GitHub Actions (ci) signal could never fire for any repo, and the workflow YAML was dropped from language stats.

Approach used: a refined Option A (data-only). The literal Option A from the suggestion ((^|/)\.github/(?!workflows/)) does NOT work here, because the directory walker prunes a subdir when IsVendored(rel + "/") matches — and .github/ (empty after the slash) still satisfies a bare negative lookahead, so the whole tree would be pruned before .github/workflows/ is ever reached. Instead used:

- "(^|/)\.github/(?!workflows(/|$))."

The trailing . requires at least one char after .github/, so the bare .github/ directory does NOT match (walker descends into it), while .github/workflows/ and its files do NOT match either (visible to InfraScanner + counted in language stats), and everything else under .github/ (issue templates, FUNDING, dependabot, docs) stays vendored. This is the data-only fix; no InfraScanner code change was needed.

Verified end-to-end with the CLI on a temp repo: infrastructure now reports GitHub Actions -> .github/workflows/ci.yml, YAML appears in languages (matching specfy's YAML: 1), .github/ISSUE_TEMPLATE is still in ignoredDirectories, and the .ipynb notebook is vendored.

Tests

dotnet test Ivy.StackAnalyzer.slnx -> Passed 95 / 95, 0 failed. No snapshot drift (no .received.yaml produced); no snapshot or test files needed updating (no existing fixture contains .github/workflows/ or the newly-vendored paths).