fix(mcp): fall back to lane cwd when source_repo is null

Adopted lanes have source_repo = null; lane-mcp.js passed it raw to
readSourceMcpServers and threw ENOMCPCONFIG. Match the existing fallback
pattern in lane-env.js/lane-profile.js.

server/__tests__/lane-mcp.test.js

@@ -79,6 +79,13 @@ describe("syncMcp — reading and relocating", () => {
       `${lane.cwd}/.playwright-mcp/profiles/default`
     );
   });
+
+  it("falls back to the lane's own cwd when source_repo is null (adopted lane)", async () => {
+    const lane = makeLane(null);
+    writeClaudeJson({ [lane.cwd]: { mcpServers: { playwright: { command: "npx", args: [] } } } });
+    const result = await laneMcp.syncMcp(lane);
+    assert.deepEqual(result.servers, ["playwright"]);
+  });
 });
 
 describe("syncMcp — Playwright output-dir pinning", () => {

server/lib/lane-mcp.js

@@ -120,8 +120,9 @@ function excludeFromGit(laneDir, line) {
  * @returns {{servers: string[], profilesSeeded: string[]}}
  */
 async function syncMcp(lane) {
-  const sourceServers = readSourceMcpServers(lane.source_repo);
-  const relocated = relocate(sourceServers, lane.source_repo, lane.cwd);
+  const sourceRepo = lane.source_repo || lane.cwd;
+  const sourceServers = readSourceMcpServers(sourceRepo);
+  const relocated = relocate(sourceServers, sourceRepo, lane.cwd);
   pinPlaywrightOutputDir(relocated, lane.cwd);
 
   fs.writeFileSync(
@@ -130,7 +131,7 @@ async function syncMcp(lane) {
   );
   excludeFromGit(lane.cwd, ".mcp.json");
 
-  const profilesSeeded = seedProfiles(lane.source_repo, lane.cwd);
+  const profilesSeeded = seedProfiles(sourceRepo, lane.cwd);
 
   return { servers: Object.keys(relocated), profilesSeeded };
 }