feat: add audited privileged trace payloads

[Super-Sky]

Summary

• add an opt-in privileged trace payload plane for model, tool, and context assembly details
• redact forbidden fields/content before AES-256-GCM encryption, authenticate retention metadata, and enforce sampling, per-record/per-run budgets, workspace switches, and short retention
• expose run/ref-bound, no-store Control Plane reads with fail-closed durable access audit while keeping app-facing timelines reference-free
• add the on-demand Control Plane inspector and integrate the existing Taste observability UI refinements

Security boundary

• disabled by default and requires a dedicated random secret of at least 32 bytes plus a key ID
• structured attachment bodies, credentials, authorization, brokerage accounts, hidden reasoning, and configured denylist fields are excluded or redacted before persistence
• Control Plane is currently a platform-admin trust boundary; every read attempt records session hash, remote IP, outcome, and returned byte count

Verification

• env -u APP_ENV go test -timeout 300s ./...
• go test -race -timeout 300s -run 'Privileged|TimelinePayloadReference' ./internal/runtime ./internal/server
• go vet ./internal/runtime ./internal/app ./internal/server
• PostgreSQL integration with concurrent per-run budget contention
• bundled Node npm ci and npm run build
• absolute-path gate and its unit tests
• PostgreSQL + OpenAI-compatible provider API/browser smoke: on-demand detail, no app payload_ref, no plaintext ciphertext, durable success audit, no test-secret leak
• benchmark: 18.3-40.6 ms/op, about 15.3 KiB/op, 54 allocs/op on the throttled local Intel baseline

Review notes

An independent adversarial review identified metadata-tampering, weak-key, sensitive free-text, UI stale-response, and lock-copy risks. This branch addresses them with authenticated AAD metadata, a 32-byte deployment-key gate, defense-in-depth content patterns, request generation checks, pointer graph receivers, and regression coverage.

Refs #30
Refs #11