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.

server/index.js

@@ -89,6 +89,7 @@ const remoteSourcesRouter = require("./routes/remote-sources");
 const metricsRouter = require("./routes/metrics");
 const lanesRouter = require("./routes/lanes");
 const projectsRouter = require("./routes/projects");
+const laneSourcesRouter = require("./routes/lane-sources");
 const locksRouter = require("./routes/locks");
 
 const APP_VERSION = (() => {
@@ -128,6 +129,8 @@ function createApp() {
   app.use("/api/git-credentials", gitCredentialsRouter);
   app.use("/api/ai-tools", aiToolsRouter);
   app.use("/api/run", runRouter);
+  // Before the lanes router, whose `/:id/:action` would otherwise see these.
+  app.use("/api/lanes", laneSourcesRouter);
   app.use("/api/lanes", lanesRouter);
   app.use("/api/projects", projectsRouter);
   app.use("/api/locks", locksRouter);