review: fix 26 findings from a 4-agent audit

CORRECTNESS
- lost-lease race: complete()/fail() did not check ownership, so a worker whose
  lease expired could mark a task done while another worker was running it, or
  requeue a task someone else owned. Reproduced, fixed with a CAS on
  (state, locked_by), pinned by two regression tests.
- worker died on report failure: _run_one's docstring claimed no exception
  escapes the TaskGroup; fail()/complete() were outside the guarded block, so a
  DB blip cancelled every sibling provision on the pod.
- claim query used an INNER join, which could strand a just-claimed task and
  report 'queue empty'. LEFT join.
- InstanceRepo.set_error bypassed the state machine and had no callers. Deleted.
- handle_deprovision ignored its CAS result, so a wrong-state instance kept a
  dangling endpoint and got re-provisioned by the drift check 60s later.
- handle_verify re-notified on every retry: five pages for one halt.

DEPLOY-BREAKING
- the migration Job could never succeed: no Dockerfile copied migrations/, and
  migrate.py resolved the path relative to the source tree, which only works for
  an editable install. Added COPY + SVCFORGE_MIGRATIONS_DIR.
- ServiceMonitor selector did not match the Service: API metrics never scraped.
- SvcforgeReconcilerStale fired permanently from every pod, because the gauge is
  module-level and every service exports it as 0. Scoped to the reconciler job.
- SvcforgeTaskFailed latched forever on a monotonic counter. Now increase()[15m].
- the digest guard accepted the all-zeros placeholder.
- worker terminationGracePeriodSeconds was 60s against a 600s helm timeout.

DEAD CODE THAT SHOULD NOT HAVE BEEN
- adapters/k8s.py was never called, so tenant namespaces were never created and
  the first provision for a new team would fail. Wired into handle_provision.
- adapters/redis.py was never imported by any service. Rate limiting is now wired
  into the API, failing open.
- Settings.check_production() had no callers. Given an explicit environment and
  called from every entrypoint.

OBSERVABILITY
- the API never called obs.setup(): no JSON logs, no trace correlation, log_json
  silently inert.
- LogNotifier's structured fields were discarded by the stdlib->structlog bridge.
- bind_task_context cleared the 'service' binding for the life of every task.
- split tasks_failed into task_attempts_failed and tasks_dead_lettered.

SECURITY
- trivy correctly blocked the worker/reconciler images: helm 3.16.2 and kubectl
  1.31.2 carry CRITICAL Go stdlib CVEs. Bumped to helm 3.21.3 and kubectl 1.35.3,
  which also closes a four-minor skew against the v1.35.3 cluster.

TESTS THAT COULD NOT FAIL
- the concurrency cap test passed on a fully serial worker.
- the alert/metric cross-check asserted a hardcoded list instead of reading the
  chart, so it could not catch a rename on the chart side.
- fixed OTel tracer-provider pollution between test files.

DOCS
- ARCHITECTURE.md: mermaid diagrams, user stories, and the helm-vs-ArgoCD
  guarantee (verified with --dry-run=server).
- AGENTS.md + CLAUDE.md.
- prose sweep for back-and-forth phrasing across 19 files.

deploy/chart/templates/_helpers.tpl

@@ -53,8 +53,18 @@ comments — the acceptance gate greps for it and does not know what a comment i
 {{- if not $img -}}
 {{- fail (printf "no image config for component %q" .component) -}}
 {{- end -}}
-{{- if not (hasPrefix "sha256:" ($img.digest | default "")) -}}
-{{- fail (printf "image.%s.digest must be a sha256 digest, not a tag — CI bumps it; got %q" .component ($img.digest | default "<empty>")) -}}
+{{- $digest := $img.digest | default "" -}}
+{{/*
+Full-shape match, not `hasPrefix "sha256:"`. A prefix check accepts the all-zeros
+placeholder in values.yaml, so a fresh clone rendered clean and the guard guarded nothing.
+Two conditions, both required: the digest must be sha256: plus exactly 64 lowercase hex
+characters, AND it must not be the placeholder literal.
+*/}}
+{{- if not (regexMatch "^sha256:[0-9a-f]{64}$" $digest) -}}
+{{- fail (printf "image.%s.digest must be a sha256 digest (sha256: + 64 hex chars), not a tag — CI bumps it; got %q" .component ($digest | default "<empty>")) -}}
+{{- end -}}
+{{- if eq $digest "sha256:0000000000000000000000000000000000000000000000000000000000000000" -}}
+{{- fail (printf "image.%s.digest is still the all-zeros placeholder from values.yaml — this chart has never been bumped by CI and must not be deployed" .component) -}}
 {{- end -}}
 {{- printf "%s@%s" $img.repo $img.digest -}}
 {{- end -}}