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>

scripts/backfill_case_status_trim.py

@@ -12,8 +12,6 @@ Mapping (removed → kept):
 
     uploading          → processing
     in_progress        → outcome_set
-    analyst_verified   → documents_ready
-    research_complete  → documents_ready
     brainstorming      → outcome_set
     analysis_enriched  → direction_approved
     ready_for_writing  → direction_approved
@@ -50,12 +48,14 @@ from legal_mcp.services import db  # noqa: E402
 logging.basicConfig(level=logging.INFO, format="%(asctime)s [%(levelname)s] %(message)s")
 log = logging.getLogger("status-trim")
 
-# removed status → nearest preceding kept status
+# removed status → nearest preceding kept status.
+# NOTE (2026-06-30): analyst_verified + research_complete were RE-CANONICALISED
+# into the status model (legal_mcp/case_status_model.py, "thinking" phase) — they
+# are valid statuses again, so they were removed from this map. Do NOT downgrade
+# them; only genuinely-removed markers remain below.
 STATUS_MAP = {
     "uploading":         "processing",
     "in_progress":       "outcome_set",
-    "analyst_verified":  "documents_ready",
-    "research_complete": "documents_ready",
     "brainstorming":     "outcome_set",
     "analysis_enriched": "direction_approved",
     "ready_for_writing": "direction_approved",