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.

docs/DATABASE.md

@@ -532,6 +532,23 @@ CREATE TABLE antigravity_conversations (
 );
 ```
 
+### lane_sources (and `lanes.instructions`)
+
+A workspace's own context, as on its home page (`server/lib/lane-sources.js`). `lanes.instructions` (TEXT, nullable, ≤ 16 000 characters) is appended to every new pane's system prompt; `lane_sources` holds its extra **folders** (the user's directories, never deleted by AgentHub) and uploaded context **files** (AgentHub's own copies under `<data dir>/workspace-context/<lane id>/`, deleted with the row and with the workspace). Both are read at spawn from these rows only (`launchExtras`), never from a request. Both are additive migrations; the rows cascade when the lane row is deleted.
+
+```sql
+CREATE TABLE lane_sources (
+    id INTEGER PRIMARY KEY,
+    lane_id INTEGER NOT NULL REFERENCES lanes(id) ON DELETE CASCADE,
+    kind TEXT NOT NULL CHECK (kind IN ('folder', 'file')),
+    path TEXT NOT NULL,     -- real path of the folder, or AgentHub's copy of the file
+    name TEXT NOT NULL,     -- folder basename / the stored file name
+    size INTEGER,           -- bytes, files only
+    added_at TEXT NOT NULL
+);
+CREATE INDEX idx_lane_sources_lane ON lane_sources(lane_id);
+```
+
 ---
 
 ## Indexes