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.

apps/web/src/globals.css

@@ -50,6 +50,9 @@
   --font-mono: "Geist Mono", ui-monospace, "SF Mono", monospace;
   --font-display: "Geist", ui-sans-serif, system-ui, sans-serif;
   --font-serif: "Instrument Serif", ui-serif, Georgia, serif;
+
+  --animate-accordion-down: accordion-down 0.2s ease-out;
+  --animate-accordion-up: accordion-up 0.2s ease-out;
 }
 
 @layer base {
@@ -149,6 +152,24 @@
   }
 }
 
+@keyframes accordion-down {
+  from {
+    height: 0;
+  }
+  to {
+    height: var(--radix-accordion-content-height);
+  }
+}
+
+@keyframes accordion-up {
+  from {
+    height: var(--radix-accordion-content-height);
+  }
+  to {
+    height: 0;
+  }
+}
+
 .animate-scroll-left {
   animation: scroll-left 30s linear infinite;
 }