feat: build an AI agent from 0 to 1 -- 11 progressive sessions

- 11 sessions from basic agent loop to autonomous teams
- Python MVP implementations for each session
- Mental-model-first docs in en/zh/ja
- Interactive web platform with step-through visualizations
- Incremental architecture: each session adds one mechanism

web/src/data/scenarios/s09.json

@@ -0,0 +1,44 @@
+{
+  "version": "s09",
+  "title": "Agent Teams",
+  "description": "Persistent teammates communicate via JSONL inboxes",
+  "steps": [
+    {
+      "type": "user_message",
+      "content": "Build a full-stack app: frontend in React, backend in Python, with tests",
+      "annotation": "Large task requiring team collaboration"
+    },
+    {
+      "type": "tool_call",
+      "content": "spawn_teammate(\n  name: \"frontend-dev\",\n  role: \"React specialist\"\n)\nspawn_teammate(\n  name: \"backend-dev\",\n  role: \"Python API specialist\"\n)",
+      "toolName": "teammate_manager",
+      "annotation": "Unlike subagents (s04) that die after one task, teammates persist"
+    },
+    {
+      "type": "system_event",
+      "content": "[TeammateManager] Team created:\n  .team/config.json written\n  frontend-dev [idle] - own thread, own agent loop\n  backend-dev [idle] - own thread, own agent loop",
+      "annotation": "Each teammate runs its own while(tool_use) loop in a separate thread"
+    },
+    {
+      "type": "tool_call",
+      "content": "send_message(\n  to: \"backend-dev\",\n  content: \"Build the user API: GET/POST /users\"\n)",
+      "toolName": "send_message",
+      "annotation": "Message appended to .team/inbox/backend-dev.jsonl"
+    },
+    {
+      "type": "system_event",
+      "content": "[backend-dev] Checking inbox... 1 new message\n  From: lead\n  Content: \"Build the user API: GET/POST /users\"\n  (inbox drained after read)",
+      "annotation": "Inbox is read-then-clear: prevents duplicate processing"
+    },
+    {
+      "type": "system_event",
+      "content": "[backend-dev -> frontend-dev] Reply via inbox:\n  \"API ready: GET /users, POST /users, GET /users/:id\"\n  Written to .team/inbox/frontend-dev.jsonl",
+      "annotation": "Teammates message each other through the same JSONL mechanism"
+    },
+    {
+      "type": "assistant_text",
+      "content": "Team is communicating via file-based inboxes. Each teammate has its own .jsonl file -- append to send, drain to read.",
+      "annotation": "JSONL inboxes decouple sender timing from receiver timing"
+    }
+  ]
+}