docs(status): align agent status maps to the canonical (nested) status model

Follow-up to the status SSoT (#382): analyst_verified + research_complete are
now first-class canonical statuses, so refresh the docs that still framed them
as legacy/decorative.

- HEARTBEAT.md §7: rewritten to point at the single source
  (case_status_model.py / GET /api/status-model), list the 12 canonical statuses
  by phase, and state the two intermediates are canonical (not legacy); genuinely
  old markers (proofread/analysis_enriched/…) are display-only fallbacks.
- legal-qa.md / legal-ceo.md status maps: dropped the "legacy/optional" framing
  on research_complete; point to the canonical model.
- scripts/backfill_case_status_trim.py: removed analyst_verified +
  research_complete from the downgrade map (they are valid statuses again — must
  NOT be downgraded) + updated the docstring.

Docs/prompts only — no behaviour change. py_compile clean.
NOTE: the host ~/legal-ai needs `git pull` for the Paperclip agents to pick up
the refreshed prompts (they run on the host tree, not the container).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/agents/legal-qa.md

@@ -179,10 +179,11 @@ tools:
 בדוק `case_get(case_number).status` — הוא צריך להיות בערכים תקפים. הזרימה הכוללת:
 
 ```
-new → proofread → documents_ready → analyst_verified → research_complete (legacy/optional)
-   → outcome_set → direction_approved → analysis_enriched → ready_for_writing
-   → drafted (אתה כאן!) → qa_passed / qa_failed → exported
+new → processing → documents_ready → analyst_verified → research_complete
+   → outcome_set → direction_approved → qa_review → drafted (אתה כאן!)
+   → exported → reviewed → final
 ```
+(מקור-אמת יחיד: `case_status_model.py` / `GET /api/status-model`. `analyst_verified`+`research_complete` קנוניים, שלב "ניתוח וכיוון". מצבי-ביניים ישנים כמו `proofread`/`analysis_enriched`/`qa_passed` נמפים-לשלב לתצוגה בלבד.)
 
 ⚠️ **`research_complete` הוא valid status** (לא bug, לא legacy ערומה). ב-`legal-researcher.md` שלב 5 הוא הסטטוס שהחוקר מגדיר בסיום מחקר. אם תיק במצב זה נשלח אליך לפני `drafted` — דווח, אל תכשיל.