feat(relay): expand role roster to dev-a through dev-f (6 devs)

Adds dev-d, dev-e, dev-f to Role type, KNOWN_ROLES, RelayQueue map,
and all three MCP tool enums in server.ts. Updates the isRole test
to assert the new roles are valid and dev-g is still rejected.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tools/relay/queue.test.ts

@@ -52,7 +52,10 @@ describe("RelayQueue", () => {
     assert.ok(isRole("dev-a"));
     assert.ok(isRole("dev-b"));
     assert.ok(isRole("dev-c"));
-    assert.ok(!isRole("dev-d"));
+    assert.ok(isRole("dev-d"));
+    assert.ok(isRole("dev-e"));
+    assert.ok(isRole("dev-f"));
+    assert.ok(!isRole("dev-g"));
     assert.ok(!isRole(""));
     assert.ok(!isRole("PM"));
   });