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.

src/db/database_manager.h

@@ -16,13 +16,23 @@ struct ProclamationRecord {
     bool is_active = true;
     bool selected = false;
     int category_id = 0;            // maps to ProclamationCategoryRecord::id
+    int group_id = 0;               // maps to ProclamationGroupRecord::id (0 = ungrouped)
     int solfeggio_frequency_id = 0; // maps to the solfeggio frequency preset
 };
 
 struct ProclamationCategoryRecord {
     int id = 0;
     std::string name;
-    int parent_id = 0; // 0 = root category
+    int sort_order = 0;
+};
+
+// A group is a tag-like organizer: it is not owned by a category. A
+// proclamation belongs to one category and may additionally belong to one
+// group. Within the UI, a group appears under a category only when at least
+// one proclamation pairs that (category_id, group_id).
+struct ProclamationGroupRecord {
+    int id = 0;
+    std::string name;
     int sort_order = 0;
 };
 
@@ -90,6 +100,9 @@ public:
     // Full sync: replaces all categories with the given set.
     bool replaceCategories(const std::vector<ProclamationCategoryRecord>& records);
 
+    // Full sync: replaces all groups with the given set.
+    bool replaceGroups(const std::vector<ProclamationGroupRecord>& records);
+
     // Full sync: upserts proclamations, deletes any not in `records`,
     // preserves the existing `selected` state, and forces the proclamation
     // identified by `defaultProclamationId` to remain selected.
@@ -102,6 +115,9 @@ public:
     // Fetch all categories ordered by sort_order then id.
     std::vector<ProclamationCategoryRecord> getAllCategories();
 
+    // Fetch all groups ordered by sort_order then id.
+    std::vector<ProclamationGroupRecord> getAllGroups();
+
     // Toggle a single proclamation's selected flag.
     bool setProclamationSelected(const std::string& id, bool selected);
 
@@ -144,6 +160,7 @@ public:
 private:
     std::string resolvePath(const std::string& raw_path) const;
     bool runMigrations();
+    bool migrateSubCategoriesToGroups();
     bool executeSql(const std::string& sql);
     bool columnExists(const std::string& table, const std::string& column);
     bool ensureColumn(const std::string& table, const std::string& column,