Slice 12: inline command-result toasts

New <toast-host> overlay: components post 'toast' CustomEvents ({message, kind: success|error|info}) and it shows brief, auto-dismissing, bottom-right toasts (errors linger). <repo-menu> (git + coordination actions) and <pr-list> (create/merge) now post friendly success/error toasts instead of alert(); the activity feed still logs everything. Also adds the slice 11 CHANGELOG entry. Verified live: 'Checked for updates' toast shown.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -243,3 +243,20 @@ Append-only running history of all changes (AGENT.md §9.1). Newest last.
   `cmd/server/main.go`, `components/pr-list`, `web/templates/help.html`,
   `AGENT.md`.
 - **Note:** the head branch must already exist on the remote (push first).
+
+## 2026-09-20 — Slice 11: branch-picker submenu
+- **What:** `<repo-menu>` "Switch branch" is now a flyout submenu populated from
+  `GET /api/repo` (the repo's branches; current one disabled), flipping leftward
+  near the viewport edge; clicking a branch checks it out. "New branch…" still
+  prompts. No backend change.
+- **Affects:** `components/repo-menu`, `web/templates/help.html`.
+
+## 2026-09-20 — Slice 12: inline command-result toasts
+- **What:** New `<toast-host>` overlay — components post `toast` CustomEvents
+  (`{message, kind}`; success/error/info) and it shows brief, auto-dismissing,
+  bottom-right toasts. `<repo-menu>` (git ops + coordination actions) and
+  `<pr-list>` (create/merge) now post success/error toasts with friendly labels
+  instead of `alert()`. Activity feed still logs everything.
+- **Why:** Immediate, legible feedback for the non-expert audience (§6 polish).
+- **Affects:** `components/toast-host` (new), `components/repo-menu`,
+  `components/pr-list`, `web/templates/index.html`.