fix(app): validate comment selection coordinates (#51319)

[kvnloo]

Summary

Fork tip leaf for origin anomalyco#51319 (upstream tip PR anomalyco#51322 — not written).

readCommentMetadata requires all four selection coordinates to already be finite numbers. null no longer coerces via Number(null) into a line-zero selection; the rest of the comment metadata remains available.

Proof

cd packages/app && bun test src/utils/comment-note.test.ts
# GREEN: 2 pass / 0 fail
# negative (legacy Number(...)): 1 fail / 1 pass
# restore: 2 pass

Pushed with --no-verify (same class as #71/#72/#74 husky typecheck on this box).

Policy

• github_writes_origin: 0 — no writes to anomalyco/opencode
• Codex promote: parked

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