feat: operationalize frontend incident runbooks

docs/runbooks/FE-RB-002.md

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+# FE-RB-002 — Chunk or deployment mismatch
+
+Trigger on `CHUNK_LOAD_FAILURE`, `RELEASE_MANIFEST_FAILURE`, or
+`DEPLOY_MISMATCH`. Warn when dirty state may be lost, fetch the manifest
+`no-store` once, record the release pair, and allow only one reload. The
+planned release-owner triage target is five minutes. Escalate to the hosting/CDN
+owner.
+
+Close only after entry/lazy assets are reachable, the manifest parses into a
+coherent tuple, a second automatic reload is blocked, and the critical route
+smoke passes.