feat(review): deterministic per-PR review-effort/complexity estimator module (1-5 band + minutes)

[JSONbored]

Core of #1955. A pure, deterministic estimator: given the changed files + patches, compute a 1-5 complexity band and a minutes estimate from files-touched, added lines (addedLineCount, src/review/review-diff.ts:25), file-type mix (classifyChangedFile, src/signals/path-matchers.ts:235), and hunk spread. No AI. This module is consumed by the ROI + unified-comment PRs; standalone + fully unit-testable.

Deliverables

• New src/review/review-effort.ts exporting estimateReviewEffort(files): { band: 1|2|3|4|5; minutes: number } — pure, deterministic, documented weighting
• Derive inputs from addedLineCount (src/review/review-diff.ts:25) and classifyChangedFile category weights (src/signals/path-matchers.ts:235); count hunks per patch for spread
• Handle edge cases explicitly: zero files, docs-only, huge single-file, many-tiny-files (each a distinct band)
• Unit tests covering every band boundary + each category weight + empty-input arm; 97% branch (test both sides of each threshold ternary)

References

• src/review/review-diff.ts:25
• src/signals/path-matchers.ts:235
• #1955

Part of #1955.

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size: S · gittensor:feature

[linear-code]

JSO-2185