Fix workflow commit atomicity, error path leak, and UI error boundary

Phase 1 of docs/reviews/2026-08-23-code-review.md.

HIGH-01: process_queued_job committed page evidence and the terminal job
status in separate transactions, so a crash between them left a transcript
persisted against a job stuck in PROCESSING that the worker never reclaims.
The final page's write is now deferred into _finalize_batch_outcome so it
shares the terminal transaction. Intermediate pages remain individually
durable, and the terminal commit is shielded against cancellation the same
way per-page writes already were.

HIGH-04: added tests/integration/test_pipeline_atomicity.py covering both
Transaction B and Transaction C. Confirmed failing against the previous
implementation before the fix.

HIGH-03: classify_unexpected_error interpolated the raw exception into
AppError.message, which the UI renders and the API serializes, leaking the
database path from OperationalError. message is now generic. Because message
also feeds format_error_detail, which writes evidence records, the root cause
is preserved on a new internal-only AppError.detail field rather than
discarded.

HIGH-02: replaced 8 hand-rolled ui.notify error calls in home_page and
people_page with error_presenter.show_error, restoring the correlation
error_id, canonical category, and suggestion. Added an AST guard to
test_ui_boundaries.py so pages cannot hand-roll error notifications again.

Docs updated per documentation-sync: the message/detail split in
docs/error_handling.md and the multi-page atomicity rule in
services.instructions.md.

Verification: ruff clean, 381 tests passing, ty unchanged at 10 known
SQLAlchemy descriptor false positives.

Co-authored-by: Copilot App <[email protected]>

.github/instructions/services.instructions.md

@@ -120,6 +120,19 @@ Atomicity rules:
 - Terminal state (`TRANSCRIBED` or `FAILED`) and transcript row changes must succeed or roll back together.
 - Retry persistence (`QUEUED` + retry increment + error detail) must succeed or roll back together.
 
+### Multi-page batches
+
+These two requirements are in tension for multi-page jobs: each page should be durable as
+soon as its provider call returns, but the last page must commit together with the terminal
+status. `process_queued_job` resolves it by committing every page except the last one
+individually, then deferring the final page's write into `_finalize_batch_outcome` so it
+shares the terminal transaction.
+
+Both paths are shielded against cancellation, so the final page is no less durable than the
+pages before it. Enforced by `tests/integration/test_pipeline_atomicity.py`; per-page
+durability is separately enforced by
+`tests/services/test_workflows_reliability.py::TestWorkflowReliability::test_transcribed_page_is_committed_before_next_provider_call_finishes`.
+
 ## Contract Alignment
 
 - Treat `docs/` as the active architecture and requirements baseline.