feat(FN-188): add Changelog tab to dashboard settings

Squash-recovery of fusion/fn-188 onto dev — original branch was based on
main (dccd4fa) due to baseBranch=None drift in Fusion settings; rebase
onto dev surfaced unrelated main-only commits (EMEX/PL24/Corgi) as false
conflicts. This commit applies only FN-188's 23-file changelog patch.

- apps/api: ChangelogModule (controller, service, DTO, spec, schema)
- apps/web: ChangelogTab (timeline + accordion), useChangelog hook, i18n
- packages/shared: changelog Zod schemas + types
- packages/ui: Accordion component + Badge stage variant
- docs/INDEX.md: changelog feature documented

Lint, typecheck, all 169 api tests + 2 web tests pass.

packages/shared/src/index.ts

@@ -29,6 +29,18 @@ export {
   forgotPasswordSchema,
   resetPasswordSchema,
 } from "./schemas/auth.js";
+export {
+  changelogStageEnum,
+  changelogEntrySchema,
+  createChangelogEntrySchema,
+  updateChangelogEntrySchema,
+} from "./schemas/changelog.js";
+export type {
+  ChangelogEntry,
+  CreateChangelogEntry,
+  UpdateChangelogEntry,
+  ChangelogStage,
+} from "./schemas/changelog.js";
 export { paginationSchema } from "./schemas/pagination.js";
 
 // Constants