feat(lanes): let claude and codex lanes coexist at the same cwd

Repo/Adopt mode (POST /api/lanes/ensure) treated lanes.cwd as globally
unique, so adopting a path already driven by one CLI silently ignored a
different tool choice. Uniqueness moves to the composite (cwd, tool):
one directory can now back a claude lane and a codex lane side by side.

- server/db.js: drop the column-level UNIQUE on cwd, migrate existing
  DBs via table rebuild, add idx_lanes_cwd_tool.
- resolveLaneByCwd gains an optional tool filter; hook ingestion always
  pins to "claude" since Codex has no hook mechanism here, so a hook
  event never touches a codex lane sharing the path.
- POST /ensure resolves the existing owner by (cwd, tool) instead of
  cwd alone, so a different tool creates a sibling lane.
- LaneConsolePane's cwd-only lane lookups now also match tool, so a
  shared cwd doesn't attach a run to the wrong sibling lane.

Worktree mode is unaffected (already allocates a unique directory per
lane). docs/LANES.md and CLAUDE.md updated to describe the new
composite uniqueness.

server/routes/lanes.js

@@ -265,7 +265,11 @@ router.post("/ensure", sameOriginGuard, (req, res) => {
     return res.status(400).json({ error: { code: "EBADTOOL", message: "unknown tool" } });
   }
 
-  const owner = lanesLib.resolveLaneByCwd(cwd);
+  // A cwd can now back one lane per tool (idx_lanes_cwd_tool) — "does a lane
+  // already own this (cwd, tool) pair" is the real question, so a request for
+  // a different tool than an existing lane at this cwd falls through to
+  // creating that tool's own lane instead of adopting the wrong one.
+  const owner = lanesLib.resolveLaneByCwd(cwd, body.tool || "claude");
   if (owner) {
     // First-write wins on the title: an ensure-with-title on an existing lane
     // is how callers like Sagi adopt the lane, so don't clobber a real title
@@ -292,7 +296,7 @@ router.post("/ensure", sameOriginGuard, (req, res) => {
     // The cwd UNIQUE constraint is the arbiter: someone else won the race, so
     // re-read and return THEIR lane rather than reporting a conflict.
     if (err.code === "SQLITE_CONSTRAINT_UNIQUE" || String(err.message).includes("UNIQUE")) {
-      const winner = lanesLib.resolveLaneByCwd(cwd);
+      const winner = lanesLib.resolveLaneByCwd(cwd, body.tool || "claude");
       if (winner) return res.json({ lane: payload(winner), created: false });
     }
     return res.status(500).json({ error: { code: err.code, message: err.message } });