feat(suggested-fix): add applied_pending status for deferred verification

Engineer applies a fix but can't verify yet (waiting on client power-cycle,
AD replication, async sync). Today the verifying banner forces a synchronous
verdict (worked / didn't / partial) — anything else means leaving the banner
stale or guessing wrong. This adds a fourth outcome that parks the fix in a
non-terminal "Awaiting verification" state with a reason ("waiting on what?")
and exposes it on the chat-anchored banner so the engineer doesn't lose track.

Backend
- New non-terminal status `applied_pending` parallel to `applied_partial`.
- New `pending_reason` column (nullable Text) — the "what are you waiting on?"
  prose, mirrors `partial_notes`. Required when outcome=applied_pending.
- Outcome endpoint allows pending in/out transitions; pending stamps
  applied_at but NOT verified_at (it's parked, not verified).
- Resolution-note + escalation-package prompts handle the new status:
  resolution note frames the fix as provisional; escalation package surfaces
  pending verification as the leading hypothesis with reference to what's
  being waited on.
- Migration: add column + extend status CHECK constraint.

Frontend
- New `BannerMode = 'pending'` + `PendingBanner` component (info-tone,
  parallel to PartialBanner) with worked / didn't / update-reason actions.
- VerifyingBanner overflow menu adds "Waiting to verify…".
- Nudge banner's "Still checking" button now actually records pending with
  a reason, instead of just silencing for the session.
- AssistantChatPage banner-mode derivation maps applied_pending → 'pending'.

Tests: 4 new integration tests covering pending notes requirement, reason
storage + applied_at/verified_at semantics, pending→success transition,
and pending_reason update on re-PATCH.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/session_suggested_fixes.py

@@ -318,6 +318,11 @@ async def patch_suggested_fix_outcome(
             status_code=status.HTTP_400_BAD_REQUEST,
             detail="notes are required when outcome is applied_partial",
         )
+    if body.outcome == "applied_pending" and not (body.notes and body.notes.strip()):
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="notes are required when outcome is applied_pending",
+        )
 
     TERMINAL = {"applied_success", "applied_failed", "dismissed"}
     if fix.status in TERMINAL:
@@ -329,6 +334,10 @@ async def patch_suggested_fix_outcome(
     fix.status = body.outcome
     if body.outcome == "applied_partial":
         fix.partial_notes = (body.notes or "").strip() or None
+    elif body.outcome == "applied_pending":
+        # Pending is parked, not terminal — keep applied_at, do NOT stamp
+        # verified_at. Reason explains what the engineer is waiting on.
+        fix.pending_reason = (body.notes or "").strip() or None
     elif body.outcome == "applied_failed":
         fix.failure_reason = (body.notes or "").strip() or None
         fix.verified_at = now