v0.8.4

Release v0.8.4

Fix editing-status drift after batched phases finish.

Two related bugs kept the phase-completion state out of sync with
actual progress, causing files to appear 'Pending' after the harness
had already finished them:

1. The batching harness never set the phase-complete flag on the
   final batch (except for prose_polish which had its own fallback).
   Small files that fit in one batch were even worse — they skipped
   the batch machinery entirely and had no completion writer at all.
   The system relied on the coordinator to notice a tool-result string
   and issue update_file_status by hand; when the coordinator forgot,
   the file stayed stuck at 'proofreading pending' with all batches
   complete.

2. Proofreading completion used two field names. The reader path
   (readEditingStatus, get_next_editing_step, aggregate stats, and
   the Zod schema itself) checked 'proofread_complete'. The writer
   path since v0.8.2 wrote 'proofreading_complete' to a different
   field the reader never looked at. Result: harness set the flag,
   reader reported 'Pending', coordinator issued a redundant
   update_file_status that happened to write the correct field —
   masking the bug most of the time and making it look like a
   coordinator memory issue.

Same class of bug hit 'last_edited_phase': only ever updated by
update_file_status, so files completed by the harness alone kept
the previous phase's value (e.g. showing 'readability' after a
successful proofread).

Fix:

• New phaseCompleteField(phase) helper maps 'proofreading' to the
  canonical 'proofread_complete'; other phases pass through. Every
  writer routes through this helper so future name drift can only
  happen in one place.
• New markPhaseComplete helper called from the non-batched path of
  all four batched specialists (dialog, style, readability,
  proofreading). Idempotent — only no-ops when both the completion
  flag AND last_edited_phase are correct, so stale values from
  previous versions get repaired on the next specialist run.
• Both completeBatch and setupBatching now set last_edited_phase
  when marking a phase complete.
• Reset map in index-tools switched to the canonical field name.

Tests: 6 new tests covering markPhaseComplete acceptance, name
mapping for proofreading, idempotency, stale-last_edited_phase
repair, and a completeBatch case locking in the field name. Total:
921 tests, all passing.

Full Changelog: v0.8.3...v0.8.4