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.

config.example.yaml

@@ -1,9 +1,9 @@
-# Fabled Scryer — Bootstrap Configuration Example
+# Roundtable — Bootstrap Configuration Example
 #
 # The only REQUIRED setting is the database URL.
 # Set it via env var (recommended for Docker):
 #
-#   FABLEDSCRYER_DATABASE_URL=postgresql+asyncpg://user:pass@host/db
+#   ROUNDTABLE_DATABASE_URL=postgresql+asyncpg://user:pass@host/db
 #
 # All other settings (SMTP, webhook, ansible, plugins, retention)
 # are stored in the database and managed via the Settings UI at /settings/.
@@ -11,7 +11,7 @@
 # config.yaml is optional. Use it only if you prefer file-based bootstrap.
 
 database:
-  url: "postgresql+asyncpg://fabledscryer:password@localhost/fabledscryer"
+  url: "postgresql+asyncpg://roundtable:password@localhost/roundtable"
 
 # Optional: override the auto-generated secret key.
 # If not set, a key is auto-generated on first run and saved to /data/secret.key.