Stage 7 (wip): docs bake + stage renumber (insert UI Stage 8, shift +1)

- PLAN.md: new Stage 8 (UI social/account/history); Telegram->9, Admin->10, Linking->11, Polish->12; tracker + Stage 7 refinements; split the Stage 6 'wired in Stage 7' note between 7 and 8
- ARCHITECTURE: promote ui to current (slice scope, board-replay, codegen, theming, mock)
- FUNCTIONAL(+ru): client-app section with the Stage 7/8 split
- README + ui/README + CLAUDE.md: UI build/run/test, codegen, pnpm notes
- bumped Stage 8-11 refs (+1) across docs and code comments

gateway/internal/admin/admin.go

@@ -2,7 +2,7 @@
 // reverse proxy to the backend admin API (docs/ARCHITECTURE.md §12). The gateway
 // validates the operator credential and forwards authenticated requests to
 // backend /api/v1/admin/*; the backend trusts the gateway on this segment. The
-// admin API itself is filled in Stage 9.
+// admin API itself is filled in Stage 10.
 package admin
 
 import (