feat(status): single source of truth for the case-status model + canonicalize intermediates

Fixes the case where the H1 chip, the pipeline stepper and the manual-changer
dropdown disagreed (e.g. 1043-02-26 on analyst_verified): the status sat between
the canonical 10 and a legacy bucket, so each surface read a different list.

Root fix — ONE authoritative status model + canonicalize the real intermediate
states (chair-approved):

- New mcp-server/.../case_status_model.py — the single registry: ordered
  StatusDef list (key/label/description/phase/selectable/terminal/on_enter),
  the 5 phases, STATUS_ORDER, phase_of/label_of, and a drift assertion that the
  CaseStatus enum matches it. `on_enter` is the seam for a status to *do*
  something on entry, declared next to its definition (no dispatcher wired yet).
- models.CaseStatus enum: analyst_verified + research_complete promoted to
  first-class canonical statuses (the agents set them — they belong in the
  model, not a legacy fallback).
- tools/cases.py: the forward-only STATUS_ORDER guard now derives from the
  registry instead of an inline list.
- GET /api/status-model exposes the model so the frontend mirror can be
  generated against it.
- web-ui case-status.ts mirrors it: the two intermediates moved from the
  legacy map into CASE_STATUSES / PHASES(thinking) / STATUS_LABELS /
  STATUS_DESCRIPTIONS; status-badge icons+tones extended. So the chip (status),
  stepper (its phase) and dropdown (now includes it) all agree.

Invariants: G2 — collapses the scattered status definitions (enum, inline
STATUS_ORDER, two frontend label maps) onto one backend authority + a documented
frontend mirror; no parallel status list remains. Agent-prompt alignment +
backfill follow in a separate change. py_compile + tsc + eslint clean.

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

web-ui/src/components/cases/status-badge.tsx

@@ -17,6 +17,8 @@ const STATUS_ICONS: Record<CaseStatus, LucideIcon> = {
   new:                FilePlus2,
   processing:         Loader2,
   documents_ready:    FileCheck,
+  analyst_verified:   SearchCheck,
+  research_complete:  Compass,
   outcome_set:        Target,
   direction_approved: Compass,
   qa_review:          SearchCheck,
@@ -36,6 +38,8 @@ const STATUS_TONE: Record<CaseStatus, string> = {
   new:               "bg-rule-soft text-ink-muted border-rule",
   processing:        "bg-info-bg text-info border-info/30",
   documents_ready:   "bg-info-bg text-info border-info/40",
+  analyst_verified:  "bg-gold-wash text-gold-deep border-gold/40",
+  research_complete: "bg-gold-wash text-gold-deep border-gold/40",
   outcome_set:       "bg-gold-wash text-gold-deep border-gold/40",
   direction_approved:"bg-gold-wash text-gold-deep border-gold/50",
   qa_review:         "bg-warn-bg text-warn border-warn/40",