refactor: centralize custom interaction IDs into constants

Replace all hardcoded custom ID strings with module-level constants.
Each module now has *_CUSTOM_IDS in its types file, using functions
for dynamic IDs and PREFIX for startsWith matching.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bot/modules/user/user.types.ts

@@ -0,0 +1,3 @@
+export const ENROLLMENT_CUSTOM_IDS = {
+    ENROLL: "enrollment",
+} as const;