fix: restore multi-workdir migration fixtures and refresh snapshots

Restore missing local session buckets under multi-workdir. Drop the
duplicate kaos non-local bucket so scans match the three-bucket fixture
contract. Refresh migration session snapshots after state writer drift.

Author: elkaix

packages/migration-legacy/test/fixtures/multi-workdir/.pythinker/pythinker.json

@@ -1,7 +1,7 @@
 {
   "work_dirs": [
-    { "path": "/proj-a", "pyaos": "local", "last_session_id": null },
-    { "path": "/proj-b", "pyaos": "local", "last_session_id": null },
-    { "path": "/proj-c", "pyaos": "pyaos-foo", "last_session_id": null }
+    { "path": "/proj-a", "kaos": "local", "last_session_id": null },
+    { "path": "/proj-b", "kaos": "local", "last_session_id": null },
+    { "path": "/proj-c", "kaos": "kaos-foo", "last_session_id": null }
   ]
 }

packages/migration-legacy/test/fixtures/multi-workdir/.pythinker/sessions/73d3cf4d1cf337adf57d6732b8be2205/uuid-a1/context.jsonl

@@ -0,0 +1,3 @@
+{"role":"_system_prompt","content":"You are a helper."}
+{"role":"user","content":"hello from a1"}
+{"role":"assistant","content":[{"type":"text","text":"hi a1"}]}

packages/migration-legacy/test/fixtures/multi-workdir/.pythinker/sessions/73d3cf4d1cf337adf57d6732b8be2205/uuid-a1/state.json

@@ -0,0 +1,10 @@
+{
+  "version": 1,
+  "approval": { "yolo": false, "auto_approve_actions": [] },
+  "additional_dirs": [],
+  "custom_title": "a1",
+  "title_generated": false,
+  "wire_mtime": 1700000000.0,
+  "archived": false,
+  "auto_archive_exempt": false
+}

packages/migration-legacy/test/fixtures/multi-workdir/.pythinker/sessions/73d3cf4d1cf337adf57d6732b8be2205/uuid-a2/context.jsonl

@@ -0,0 +1,3 @@
+{"role":"_system_prompt","content":"You are a helper."}
+{"role":"user","content":"hello from a2"}
+{"role":"assistant","content":[{"type":"text","text":"hi a2"}]}

packages/migration-legacy/test/fixtures/multi-workdir/.pythinker/sessions/73d3cf4d1cf337adf57d6732b8be2205/uuid-a2/state.json

@@ -0,0 +1,10 @@
+{
+  "version": 1,
+  "approval": { "yolo": false, "auto_approve_actions": [] },
+  "additional_dirs": [],
+  "custom_title": "a2",
+  "title_generated": false,
+  "wire_mtime": 1800000000.0,
+  "archived": false,
+  "auto_archive_exempt": false
+}