Improve redaction annotation to remove more

[JoackimPennerup]

Summary

This PR hardens annotation-mode redaction to better match Acrobat-style behavior for applied redactions and to reduce residual sensitive data in annotations/forms.

What changed

1. Intersecting annotation cleanup on apply

• When a REDACT annotation is applied, intersecting page annotations are inspected.
• Intersecting annotations are removed if they are not REDACT.

2. Intersecting form widget handling (updated behavior)

• Intersecting widgets are now removed.
• No placeholder replacement annotation is created.
• Visual result comes from redaction application itself.

3. Linked redaction thread cleanup

• Linked comment/reply thread annotations are removed via transitive inReplyToId traversal seeded from applied REDACT IDs.

4. State/history synchronization

• Annotation state, pending redaction state, and annotation history metadata are purged consistently for affected IDs (removed + applied).

5. Shared geometry intersection utility

• Added rectsIntersect(a, b) in @embedpdf/models and exported it.
• Removed duplicate local intersection logic usage in annotation helper paths.

6. PDFium checked-field deterministic behavior

• setFormFieldValue(..., { kind: 'checked', isChecked }) now toggles only when current state differs from requested state (idempotent set-to-target behavior).

Important behavior notes

• Redaction fill appearance remains controlled by redaction styling/config (including chosen color).
• Legacy mode behavior remains unchanged.

Tests

Added/updated tests covering:

• geometry intersection semantics (rectsIntersect)
• deterministic checked-field set behavior in PDFium
• redaction plugin annotation-mode behavior:
  • removes intersecting non-widget annotations
  • removes intersecting widgets
  • removes linked thread annotations
  • preserves unrelated non-intersecting annotations
  • failure path emits failed commit and avoids state/history purge

Validation

• pnpm --filter @embedpdf/plugin-redaction test ✅
• pnpm --filter @embedpdf/models test ✅
• pnpm --filter @embedpdf/engines test ✅

Out of scope / follow-up

• “Redact All” multi-page rerender/page-discovery consistency is intentionally deferred to a follow-up PR (separate concern from hardening behavior).

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[JoackimPennerup]

@bobsingor Any change you could have a look at this? I'd be happy to change it into another direction if you'd like.