feat(FN-3162): add plugin-owned roadmap schema hook and store bootstrap

The merge introduces a plugin-owned roadmap schema system (FN-3162), allowing plugins to define their own schema initialization hook, with tests bootstrapped in the roadmap store and documentation added to the plugin authoring guide. The parallel FN-3281 work delivers review revisions, updates the l

Fusion-Task-Id: FN-3162

docs/PLUGIN_AUTHORING.md

@@ -321,6 +321,7 @@ const plugin: FusionPlugin = {
 - **Schema hook execution**: `onSchemaInit` hooks run sequentially in plugin dependency order (from `resolveLoadOrder`) after `loadAllPlugins()`.
 - **Schema hook database API**: The hook receives the runtime `Database` instance, including `db.exec()` and `db.prepare()` for SQL DDL.
 - **Schema hook constraints**: `onSchemaInit` is intended for idempotent DDL only (`CREATE TABLE IF NOT EXISTS`, `CREATE INDEX IF NOT EXISTS`). Avoid data backfills or long-running logic.
+- **Bundled plugin pattern**: Keep DDL in a plugin-local schema module (for example `src/<plugin>-schema.ts`) and call it from `hooks.onSchemaInit` so schema ownership stays with the plugin package instead of `@fusion/core` bootstrap SQL.
 
 ### Example: Schema initialization hook