v1.9: settings pane + per-project defaults + bulk archive + themes lift

Adds a singleton, ephemeral 'settings' pane kind to the workspace.
Opened via a new bottom-pinned button in ProjectSidebar (emits an
open_settings_pane event when a session is mounted; navigates to
/settings otherwise). Pane has three sections — Session, Project,
Theme — and a maximize toggle that hides sibling pane columns via
display:none on desktop only. Settings panes don't count toward
MAX_PANES and are filtered out of the localStorage persistence layer
so reload always restores a clean workspace.

Schema (additive):
- projects.default_system_prompt TEXT NOT NULL DEFAULT ''
- projects.default_web_search_enabled BOOLEAN NOT NULL DEFAULT false
- sessions.web_search_enabled BOOLEAN  (nullable; null = inherit)

Inference resolves user_prompt = session.system_prompt.trim() ||
project.default_system_prompt.trim() — empty/whitespace at either
layer means "no override". Keeps the columns NOT NULL and matches
the existing inherit semantics.

Server routes:
- GET /api/projects/:id (new; settings pane refetches on
  project_updated)
- PATCH /api/projects/:id accepts default_system_prompt,
  default_web_search_enabled
- PATCH /api/sessions/:id accepts web_search_enabled (tri-state)
- POST /api/projects/:id/sessions/archive-all + GET
  /api/projects/:id/sessions/open-count
- POST /api/sessions/:id/chats/archive-all + GET
  /api/sessions/:id/chats/open-count
- PATCH /api/sessions/:id now broadcasts session_updated on every
  successful PATCH (was rename-only). Lets SettingsPane open in
  another tab pick up edits without a refetch.

Bulk-archive publishes one session_archived / chat_archived frame
per affected id so useSidebar's existing reducer cases handle them
incrementally — no new frame type, no payload widening.

ModelPicker refactored: shared ModelList inside a responsive shell.
Desktop = labeled trigger + DropdownMenu, mobile = icon-only Cpu
button + BottomSheet. Header in Session.tsx drops the pill wrap on
mobile since the new trigger is the visual.

ChatInput gains an icon-only '+' DropdownMenu next to AgentPicker
when sessionId + webSearchEnabled props are provided. One item for
now — Web search — with a checkmark reflecting the stored value
(true), not the effective one. Click PATCHes the override; to
restore inherit-from-project the user opens SettingsPane.

ThemePicker lifted out of pages/Settings.tsx into a reusable
component. The standalone /settings route is now a thin wrapper
that mounts <ThemePicker /> with a Back button on top
(navigate(-1) with fallback to '/'); the SettingsPane Theme tab
renders the same picker bare.

Project section delete-flow removed (button + confirm dialog +
handler). Replaced with "Archive all sessions" using the same
two-step count → confirm → fire pattern as "Archive all chats" in
the Session section. api.projects.remove() stays in the client
because useProjects.ts still uses it.

Hand-rolled Switch primitive in SettingsPane (no shadcn switch in
the project; spec said no new deps). Section nav is plain buttons
(no shadcn Tabs).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/api/client.ts

@@ -51,15 +51,29 @@ export const api = {
         method: 'POST',
         body: JSON.stringify(body),
       }),
-    update: (id: string, body: { name: string }) =>
+    update: (
+      id: string,
+      body: Partial<Pick<Project, 'name' | 'default_system_prompt' | 'default_web_search_enabled'>>,
+    ) =>
       request<Project>(`/api/projects/${id}`, {
         method: 'PATCH',
         body: JSON.stringify(body),
       }),
+    get: (id: string) => request<Project>(`/api/projects/${id}`),
     archive: (id: string) =>
       request<void>(`/api/projects/${id}/archive`, { method: 'POST' }),
     unarchive: (id: string) =>
       request<Project>(`/api/projects/${id}/unarchive`, { method: 'POST' }),
+    // v1.9: bulk-archive every open session in this project. Server publishes
+    // one session_archived frame per affected id, so the sidebar reducer
+    // updates incrementally rather than waiting for a refetch.
+    archiveAllSessions: (id: string) =>
+      request<{ archived: number; ids: string[] }>(
+        `/api/projects/${id}/sessions/archive-all`,
+        { method: 'POST' },
+      ),
+    openSessionsCount: (id: string) =>
+      request<{ count: number }>(`/api/projects/${id}/sessions/open-count`),
     create: (body: {
       name: string;
       commit_message?: string;
@@ -106,7 +120,7 @@ export const api = {
     get: (id: string) => request<Session>(`/api/sessions/${id}`),
     update: (
       id: string,
-      body: Partial<Pick<Session, 'name' | 'model' | 'system_prompt' | 'agent_id'>>
+      body: Partial<Pick<Session, 'name' | 'model' | 'system_prompt' | 'agent_id' | 'web_search_enabled'>>
     ) =>
       request<Session>(`/api/sessions/${id}`, {
         method: 'PATCH',
@@ -118,6 +132,15 @@ export const api = {
       request<void>(`/api/sessions/${id}/archive`, { method: 'POST' }),
     unarchive: (id: string) =>
       request<Session>(`/api/sessions/${id}/unarchive`, { method: 'POST' }),
+    // v1.9: bulk-archive every open chat in this session. Same pattern as
+    // archiveAllSessions — server publishes one chat_archived per id.
+    archiveAllChats: (id: string) =>
+      request<{ archived: number; ids: string[] }>(
+        `/api/sessions/${id}/chats/archive-all`,
+        { method: 'POST' },
+      ),
+    openChatsCount: (id: string) =>
+      request<{ count: number }>(`/api/sessions/${id}/chats/open-count`),
   },
 
   chats: {