feat(FN-1216): rename extension tools to fn_* across CLI and docs

- Rename all pi extension tool registrations from kb_* to fn_* across task, mission, and agent tool families
- Update extension and skill-sync tests plus Fusion skill docs/workflows to assert and document the new fn_* tool names
- Align product-identity strings across core, dashboard, and CLI references, including GitHub import examples, User-Agent headers, and terminal TERM_PROGRAM
- Add a @gsxdsm/fusion minor changeset describing the extension tool-prefix rename

packages/core/src/db-migrate.ts

@@ -39,7 +39,7 @@ export function detectLegacyData(kbDir: string): boolean {
 }
 
 /**
- * Get the migration status of a kb directory.
+ * Get the migration status of a fn directory.
  */
 export function getMigrationStatus(kbDir: string): {
   hasLegacy: boolean;