[Epic]: A governed observability surface — one dashboard catalogue, Copilot reporting, trace-log correlation

### Summary

One dashboard catalogue that governs both what is kept and what is added, plus the two remaining correlation and datasource gaps.

### Intent

The dashboard set has accreted to 20+ generated modules on `main` while a separate workstream proposes four more, and nothing says which are sanctioned. A pruning ticket and an addition ticket that do not know about each other produce the next accretion — so they belong under one catalogue.

### Children

- **#530** — decide and enforce the sanctioned dashboard set
- **#674** — traces-to-logs correlation
- **#879** — read-only Grafana Postgres datasource over the governance database
- **#880** — four Copilot governance dashboards and five ingestion alerts

### Acceptance Criteria

1. A catalogue at `docs/observability/dashboard-catalogue.md` lists every kept dashboard and its panel spec.
2. **CI fails when `tools/dashboards/src/dashboards/` contains a module absent from the catalogue** — a new dashboard lands by adding a catalogue row, so the set cannot silently grow again.
3. `uv run dashboards check` passes.

### Out of Scope

- Grafana provisioning mechanics and datasource plumbing beyond what #879 needs.

### Technical Context

⚠️ **#879's premise is stale**: it says "no governance database exists yet", but the `governance` role and Database are on `main` in `charts/lightbridge-db/values.yaml`, and its dependency `lightbridge-governance#12` is closed.

⚠️ **#879 is building a datasource over a database ADR-0014 decommissions.** `lightbridge-governance` consolidated its telemetry store into the authz usage store on 2026-08-31; that ADR's sweep did not reach this repo. Settle the target before building the grant — see `lightbridge-governance#197`.

⚠️ #530's current AC says "every **unplanned** dashboard is removed", measured against a local planning file not in the repo. AC 2 above replaces that with something re-readable.

### AI Usage Declaration

Grouping identified and drafted by Claude Opus 5 during the 2026-09-01 triage sweep; #879's stale premise and the ADR-0014 collision were verified against `origin/main`. AI output is not truth; the owner verifies.

Start with the acceptance criteria, docs/observability/dashboard-catalogue.md, and tools/dashboards/src/dashboards/; review child issues #530, #674, #879, and #880 before changing anything. Run `uv run dashboards check` and verify the catalogue covers every dashboard module, CI rejects unlisted modules, and the datasource target is settled against the referenced ADR and governance issue.

Escrito por el modelo de indexación a partir del texto del issue.