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.

README.md

@@ -56,10 +56,16 @@ Internal build — all rights reserved.
 
 **Configure**
 
+- **Workspaces like Claude Desktop projects.** The sidebar lists every
+  workspace with its sessions under it (a live one opens its tmux pane, any
+  other its transcript — never a resume). A workspace opens on its home: a
+  prompt box that starts a new session, Recents, and the workspace's own
+  Instructions, Memory, Context files and extra Folders, which Claude and Codex
+  sessions start with.
 - **Settings as one page per section** (`/settings/<section>`): a left nav
-  grouped General / Agents / Routing / Git / Projects, a search box (Ctrl+F)
-  over every section, a page per installed AI tool, per-vendor model pricing,
-  which untracked worktrees the sidebar lists, and a page per project.
+  grouped General / Agents / Routing / Git, a search box (Ctrl+F) over every
+  section, a page per installed AI tool, per-vendor model pricing, and which
+  untracked worktrees a workspace's Add folder suggests.
 - **Claude Code + Codex configuration explorer.** Settings hosts one page per
   tool: every plugin, skill, subagent, slash command, MCP server, hook, settings
   file, memory file, marketplace, keybinding and statusline Claude Code knows