feat(pilot): Phase 4 — Resolve + Escalate PSA writebacks with status verification

Wires the preview popover's Confirm & post action to ConnectWise (and,
via the provider pattern, any future PSA). Adds the parallel Escalate
flow with the handoff-oriented five-section markdown. Sessions without a
linked PSA ticket resolve/escalate locally — markdown stored, status
flipped, nothing posted externally.

Backend:
- EscalationPackageGeneratorService: Sonnet, five sections (Problem /
  What we've confirmed / What we've tried / Current hypothesis /
  Suggested next steps). Shares the preview_cache with a separate KIND
  so Resolve and Escalate previews for the same state coexist.
- PSAWritebackService: post_resolution_note (RESOLUTION note type,
  customer-visible), post_escalation_package (INTERNAL_ANALYSIS,
  handoff for the next engineer only), transition_ticket_status with
  mandatory re-fetch verification. PSAStatusVerificationError surfaces
  loudly when CW silently rejects a status change — the
  ConnectWise anti-pattern CLAUDE.md flags.
- Endpoints:
  * POST /ai-sessions/{id}/escalation-package/preview
  * POST /ai-sessions/{id}/resolution-note/post
  * POST /ai-sessions/{id}/escalation-package/post
  Outcomes: "resolved" / "escalated" with external_id + verified status,
  "resolved_local" / "escalated_local" when no PSA linked.
- Target CW status IDs live in account_settings.preferences
  (cw_resolved_status_id, cw_escalated_status_id). When unset, the post
  proceeds without a status transition — response includes a
  status_transition_skipped_reason rather than silently erroring.
- 7 tests: local-only path, PSA happy path with verified transition,
  status verification failure → 502, skipped transition when
  unconfigured, 409 on already-resolved re-post, escalate parallel path,
  internal-analysis note type enforced.

Frontend:
- ResolutionNotePreview now kind-parameterized ('resolve' | 'escalate')
  with inline edit + Confirm & post. Preview loads from the matching
  backend endpoint; posting calls the matching endpoint; outcome toast
  surfaces the verified CW status or the local-only result.
- AssistantChatPage: previewKind state replaces previewOpen; two toggle
  buttons (Preview Resolve note / Escalate instead) in the lane's bottom
  slot. handleConfirmPost dispatches by kind.

Verified 2026-04-22:
- Local-only Resolve + Escalate round-trip against the dev stack.
- Live Sonnet escalation-package preview; cache hit on repeat call
  with no state change (separate cache kind from resolution-note).
- PSA post + status-verification paths covered by mocked-provider pytest
  cases. Live CW round-trip pending a test CW instance.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/schemas/session_suggested_fix.py

@@ -61,3 +61,35 @@ class ResolutionNotePreviewResponse(BaseModel):
     target_ticket_ref: str | None
     state_version: int
     from_cache: bool
+
+
+# ── Phase 4: Resolve + Escalate post ───────────────────────────────────────
+
+class ResolutionNotePostRequest(BaseModel):
+    """Engineer-edited resolution markdown. Server posts to PSA + marks resolved."""
+    markdown: str = Field(..., min_length=1, max_length=20_000)
+    # Optional override for resolution summary shown on the session listing;
+    # defaults to the first line of the markdown if omitted.
+    resolution_summary: str | None = Field(None, max_length=500)
+
+
+class EscalationPackagePostRequest(BaseModel):
+    markdown: str = Field(..., min_length=1, max_length=20_000)
+    # Free-text reason shown in session listings and escalation queue.
+    escalation_reason: str | None = Field(None, max_length=500)
+
+
+class ResolutionPostResponse(BaseModel):
+    """Response shape for both Resolve/Escalate POST endpoints."""
+    # "resolved" / "escalated" / "resolved_local" / "escalated_local"
+    # The _local variants indicate the session has no linked PSA ticket —
+    # markdown is stored, session state is updated, nothing was posted externally.
+    outcome: str
+    session_status: str
+    external_id: str | None = None
+    posted_at: datetime | None = None
+    # Populated when a status transition was attempted and verified. None
+    # when no target status is configured in account_settings.preferences.
+    verified_status_id: int | None = None
+    verified_status_name: str | None = None
+    status_transition_skipped_reason: str | None = None