Avoid re-running the AI pipeline on derived artifacts

[JosephLeon]

Five complementary changes so users stop accidentally re-paying for transcription + classification on content the pipeline already saw.

Pattern 1+6 (render-lineage detection on add):

• New renderLineage.ts walks the active project's render_history when a user drags in a file. If the path matches an entry's output, the AddPanel routes through a new "That's one of your renders" modal instead of the normal copy/reference flow.
• "Continue editing intro.mov" jumps the AI tab to the original source via setActive(), so the next render reuses cached artifacts.
• "Add anyway" stays as an escape hatch.

Pattern 2 (UI copy):

• Pacing tab + Audio tab render buttons now spell out "No AI cost on re-render": cuts and overrides reuse the cached classification; audio enhancement / denoise / ducking never touch the LLM.

Pattern 4 (content-hash cache for /analyze):

• New _analysis_cache.py keys cached AnalysisBundle JSONs by SHA256 of the extracted mic WAV. /analyze hashes after ingest (~1s), looks up, and skips the Groq call on hit. Cache miss falls through to the normal Whisper pass and stores the result.
• Catches re-imports, copies across projects, symlinks of the same audio. Doesn't catch trims / different mic tracks (correctly).
• Saves ~$0.05 per duplicate analyze.

Pattern 5 (no code changes):

• Verified runAllStages is idempotent on completed stages and that override / custom-cut mutations route only through the store + /render's re-plan path, never re-triggering /classify.

Pattern 3 (deferred):

• Splice-aware Cadence (talking to the model about a spliced output without re-running transcription on each clip) is real architecture work: artifact builder with offset math, dispatcher routing, custom cuts at splice-time. Full design captured in docs/design-splice-classification-reuse.md for a future PR.

Drive-bys: re-applied two tsc -b strict-mode fixes (SplicingView discriminated-union narrowing + projectDigest export-type) that lived on the deleted public-release branch and didn't make it to master.

What this changes

Why

How I tested

Anything reviewers should pay attention to

Checklist

• Added/updated tests for new pure-logic helpers (tests/)
• uv run pytest passes locally
• bun run tsc --noEmit passes locally (if frontend touched)
• Type hints on new Python; strict TypeScript on new TS
• No new dependencies, or the new dep is justified above
• No secrets / personal paths in the diff