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/alembic/versions/71efd2102f49_add_pending_status_to_suggested_fixes.py

@@ -0,0 +1,60 @@
+"""add applied_pending status + pending_reason to session_suggested_fixes
+
+Adds the `applied_pending` non-terminal status (engineer ran the fix but
+verification is deferred — waiting on client, async sync, etc) alongside
+the existing `applied_partial` status. Mirrors partial_notes with a new
+pending_reason column for the "what are you waiting on?" prose.
+
+Revision ID: c0f3a4b7e91d
+Revises: 71efd2102f49
+Create Date: 2026-04-30
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = "c0f3a4b7e91d"
+down_revision: Union[str, None] = "71efd2102f49"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "session_suggested_fixes",
+        sa.Column("pending_reason", sa.Text(), nullable=True),
+    )
+    op.drop_constraint(
+        "ck_session_suggested_fixes_status",
+        "session_suggested_fixes",
+        type_="check",
+    )
+    op.create_check_constraint(
+        "ck_session_suggested_fixes_status",
+        "session_suggested_fixes",
+        "status IN ('proposed', 'applied_success', 'applied_failed', "
+        "'applied_partial', 'applied_pending', 'dismissed')",
+    )
+
+
+def downgrade() -> None:
+    op.execute(
+        "UPDATE session_suggested_fixes "
+        "SET status = 'applied_partial', "
+        "    partial_notes = COALESCE(partial_notes, pending_reason) "
+        "WHERE status = 'applied_pending'"
+    )
+    op.drop_constraint(
+        "ck_session_suggested_fixes_status",
+        "session_suggested_fixes",
+        type_="check",
+    )
+    op.create_check_constraint(
+        "ck_session_suggested_fixes_status",
+        "session_suggested_fixes",
+        "status IN ('proposed', 'applied_success', 'applied_failed', "
+        "'applied_partial', 'dismissed')",
+    )
+    op.drop_column("session_suggested_fixes", "pending_reason")