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.

scripts/hook-handler.js

@@ -60,6 +60,9 @@ process.stdin.on("end", () => {
     hook_type: hookType,
     data: parsedData,
     ...(tool && { tool }),
+    // Set in every pane the dashboard starts (server/lib/pty-run.js): names
+    // the pane this session runs in. Absent in a user's own terminal.
+    ...(process.env.AGENTHUB_RUN_ID && { run_id: process.env.AGENTHUB_RUN_ID }),
   });
   const contentLength = Buffer.byteLength(payload);