docs: roundtable rename sweep

Sweeps README, docs/, example configs, code docstrings, report and
notification subject lines, plugin catalog URL default, and stray
comments in Dockerfile/entrypoint.sh/.gitignore. Adds a legacy note
to docs/core/configuration.md explaining the FABLEDSCRYER_* fallback.
docker-compose DB credentials intentionally left as fabledscryer to
preserve the existing pgdata volume.

docs/core/alerting.md

@@ -14,7 +14,7 @@ When any monitor or plugin calls `record_metric()`:
 4. If a state transition occurs, an `AlertEvent` row is written
 5. Notification I/O is deferred outside the transaction via `asyncio.create_task()`
 
-**Key function:** `fabledscryer/core/alerts.py` → `record_metric(session, source_module, resource_name, metric_name, value)`
+**Key function:** `roundtable/core/alerts.py` → `record_metric(session, source_module, resource_name, metric_name, value)`
 
 `record_metric()` must always be called inside an active transaction:
 
@@ -130,7 +130,7 @@ Webhook is skipped if `webhook.url` is empty.
 
 ## Data Models
 
-Defined in `fabledscryer/models/alerts.py`:
+Defined in `roundtable/models/alerts.py`:
 
 - **`alert_rules`** — one row per configured rule
 - **`alert_states`** — one row per rule, tracks current state and consecutive failure count