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/server/src/routes/chats.ts

@@ -123,6 +123,53 @@ export function registerChatRoutes(
     }
   );
 
+  // v1.9: bulk-archive every open chat in a session. Mirrors the single
+  // /chats/:id/archive shape — N chat_archived frames published, useSidebar
+  // reducer handles each via the existing case.
+  app.post<{ Params: { id: string } }>(
+    '/api/sessions/:id/chats/archive-all',
+    async (req, reply) => {
+      const session = await sql`SELECT id FROM sessions WHERE id = ${req.params.id}`;
+      if (session.length === 0) {
+        reply.code(404);
+        return { error: 'session not found' };
+      }
+      const rows = await sql<{ id: string }[]>`
+        UPDATE chats
+           SET status = 'archived', updated_at = clock_timestamp()
+         WHERE session_id = ${req.params.id} AND status = 'open'
+         RETURNING id
+      `;
+      const ids = rows.map((r) => r.id);
+      for (const id of ids) {
+        broker.publishUser('default', {
+          type: 'chat_archived',
+          chat_id: id,
+          session_id: req.params.id,
+        });
+      }
+      return { archived: ids.length, ids };
+    }
+  );
+
+  // v1.9: count helper for the confirm dialog.
+  app.get<{ Params: { id: string } }>(
+    '/api/sessions/:id/chats/open-count',
+    async (req, reply) => {
+      const session = await sql`SELECT id FROM sessions WHERE id = ${req.params.id}`;
+      if (session.length === 0) {
+        reply.code(404);
+        return { error: 'session not found' };
+      }
+      const rows = await sql<{ count: number }[]>`
+        SELECT COUNT(*)::int AS count
+          FROM chats
+         WHERE session_id = ${req.params.id} AND status = 'open'
+      `;
+      return { count: rows[0]?.count ?? 0 };
+    }
+  );
+
   app.post<{ Params: { id: string } }>(
     '/api/chats/:id/archive',
     async (req, reply) => {