fix(hooks): store a hook delivered twice only once

A doubled hook registration (plugin + leftover checkout install) POSTs every
event twice with a byte-identical payload, so the timeline showed each row
twice and token/alert/lane side effects ran twice. POST /api/hooks/event now
skips a payload identical to the session's LATEST event from the last 10s
(findRecentDuplicateEvent). Latest-only keeps two legitimately identical
Stop events of consecutive turns, which always have other events between.

server/__tests__/session-name-rename.test.js

@@ -172,7 +172,7 @@ describe("hook ingestor — sessions.name sync from transcript", () => {
     ]);
     await req("POST", "/api/hooks/event", {
       hook_type: "Stop",
-      data: { session_id: sid, cwd, transcript_path: tpath },
+      data: { session_id: sid, cwd, transcript_path: tpath, turn: 1 },
     });
     assert.equal(stmts.getSession.get(sid).name, "keep-me");
 
@@ -184,7 +184,7 @@ describe("hook ingestor — sessions.name sync from transcript", () => {
     ]);
     await req("POST", "/api/hooks/event", {
       hook_type: "Stop",
-      data: { session_id: sid, cwd, transcript_path: tpath },
+      data: { session_id: sid, cwd, transcript_path: tpath, turn: 2 },
     });
     assert.equal(stmts.getSession.get(sid).name, "renamed-explicitly");
   });