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/proclamation_options_page.h

@@ -28,13 +28,13 @@ public:
 
 private:
     struct FlatItem {
-        enum class Type { RootCategory, SubCategory, Proclamation };
+        enum class Type { Category, Group, Proclamation };
 
         Type type = Type::Proclamation;
-        std::string id;         // category id or proclamation id
+        std::string id;         // category id, group id, or proclamation id
         std::string label;      // display text
-        int depth = 0;          // 0 = root category / default, 1 = sub-category, 2 = proclamation
-        bool expanded = false;  // categories only
+        int depth = 0;          // 0 = category / default, 1 = group, 2 = proclamation
+        bool expanded = false;  // categories and groups only
         bool selected = false;  // proclamations only
         bool isDefault = false; // the always-on top-level proclamation
     };
@@ -67,6 +67,7 @@ private:
     AppState* state_ = nullptr;
     std::vector<radiantwave::db::ProclamationRecord> proclamations_;
     std::vector<radiantwave::db::ProclamationCategoryRecord> categories_;
+    std::vector<radiantwave::db::ProclamationGroupRecord> groups_;
     std::vector<FlatItem> items_;
     std::vector<size_t> visible_;       // indices into items_, in display order
     std::vector<size_t> searchResults_; // indices into proclamations_, search mode