feat(ui): a Claude-Desktop-style home for every workspace

/workspace?lane=<id> opens on the workspace's home (WorkspaceHome): a prompt
box whose Start opens a new session in the first free pane slot, Recents (a
live session attaches its pane, any other opens its transcript, nothing
resumes), and Instructions / Memory / Context / Folder. Instructions live in
lanes.instructions, extra folders and uploaded files in the new lane_sources
table (copies under <data dir>/workspace-context/<lane id>/); spawnRun reads
them from the lane's rows and hands Claude --add-dir + an appended system
prompt file, Codex --add-dir + developer_instructions. Memory is read-only.

Every dashboard pane carries AGENTHUB_RUN_ID; hooks forward it and the run
records which session the pane holds (a Claude pane follows /clear and
/resume but not a nested claude -p), so the sidebar and notifications open
the right pane (&run=). Settings loses its Projects group; Worktrees now
decides which worktrees Add folder suggests.

client/README.md

@@ -184,6 +184,7 @@ client/
 │   │   ├── EmptyState.tsx
 │   │   ├── Sidebar.tsx
 │   │   ├── WorkspaceTree.tsx  # Sidebar Workspaces list: one row per workspace, expanding to its sessions (live → its pane, else the transcript), row menu
+│   │   ├── lanes/WorkspaceHome.tsx  # /workspace?lane=<id>: prompt box (new session in a free pane slot), Recents, Instructions / Memory / Context / Folder
 │   │   ├── StatusBar.tsx    # Fixed bottom bar: Live/Disconnected, version, running / needs-you counts, today's cost
 │   │   ├── Layout.tsx
 │   │   ├── RemoteSources.tsx  # Remote Data Sources settings panel (SSH multi-machine collection)
@@ -252,7 +253,7 @@ graph TB
     Detail[SessionDetail<br/>agent hierarchy + timeline]
     Feed[ActivityFeed<br/>streaming event log]
     Workflows[Workflows<br/>Analytics → Workflow sub-tab:<br/>lane pipelines + D3 analytics]
-    Settings[SettingsHub /settings/:section<br/>General · Appearance · Notifications<br/>Agents: AI tools, Claude Code, Codex, each catalog tool<br/>Routing: AI Router, Pricing · Git: credentials, worktrees<br/>Projects: one page per repo]
+    Settings[SettingsHub /settings/:section<br/>General · Appearance · Notifications<br/>Agents: AI tools, Claude Code, Codex, each catalog tool<br/>Routing: AI Router, Pricing · Git: credentials, worktree suggestions]
 
     App --> Layout
     Layout --> Dashboard & Sessions & Detail & Feed & Settings
@@ -473,7 +474,7 @@ graph TB
     CcConfig["/cc-config (redirect)"]
     Lanes["/lanes (redirect)"]
     Run["/run (redirect)"]
-    Workspace["/workspace?lane=<id>"]
+    Workspace["/workspace?lane=<id> (home) · &run=<runId> (session)"]
     Settings["/settings (tabs: dashboard | claude-code | ...)"]
     NF["/* (NotFound)"]