Move Proclamations From Sub-Categories To Groups

The portal's v2 API replaced nested categories (proclamation_categories.parent_id)
with flat categories plus tag-like groups: a proclamation now belongs to one
category and optionally one group. This lets the Proclamation Options page drop
its special-cased two-level tree.

Database:
- Add the proclamation_groups table (id, name, sort_order) and a
  proclamations.group_id column.
- Drop parent_id from the proclamation_categories DDL so fresh databases get a
  flat table.
- runMigrations() creates the new table/column, then runs a one-time
  transactional v1->v2 migration keyed on PRAGMA user_version: every legacy
  sub-category becomes a group (its id is preserved), proclamations that
  pointed at a sub-category are remapped to (parent category, new group), and
  the now-stale sub-category rows are deleted. selected flags are never
  touched, so user choices survive. No network is needed, so offline kiosks
  migrate at startup; re-running is a no-op.
- Add replaceGroups() and getAllGroups(); stop reading/writing parent_id.

API sync:
- Add PATH_GROUPS ("/groups") and parseGroupsJson().
- parseProclamationsJson() now also reads groupId.
- syncProclamationsFromApi() fetches /proclamations, /categories and /groups,
  leaves the database untouched if any request or parse fails, then replaces
  categories, replaces groups and upserts proclamations.

Proclamation Options page:
- FlatItem is now Category / Group / Proclamation.
- Each category lists only the groups that have at least one member in that
  category, so impossible pairings (e.g. Physical/Prayers) never render.
- Proclamations with no group, or with a group the portal has removed, sit
  directly under the category. Groups are collapsible and use a distinct color.

Tests:
- test_db: groups round-trip plus a legacy->v2 migration test asserting the
  group is created, proclamations are remapped, selection is preserved and a
  second initialize() is a no-op.
- test_proclamation_sync / test_api_client: parse groupId, parse groups, and
  the live smoke test now also fetches /groups.

Docs: README database table and AGENTS notes updated for groups.

README.md

@@ -484,8 +484,9 @@ SQLite at `~/.local/share/radiantwave/database.sqlite` (WAL mode).
 | ------- | --------- |
 | app_config | Key-value store: license, email, audio device, volume |
 | logs | Application logs |
-| proclamations | Synced proclamation text |
-| proclamation_categories | Category metadata |
+| proclamations | Synced proclamation text (category_id + group_id) |
+| proclamation_categories | Flat category metadata |
+| proclamation_groups | Tag-like groups that organize proclamations within a category |
 | solfeggio_frequencies | 9 frequency presets |
 | audio_files | Downloaded audio files |