Refactor: single collection with shared/private visibility

Breaking change: per-agent collections replaced by a single 'memories'
collection with metadata-based access control.

- All memories live in one collection
- 'agent' metadata tracks the creator
- 'private' (bool, default False) controls visibility
- Query returns: shared (private=False) + own private (agent=asker)
- Save endpoint accepts optional 'private' field
- Version bumped to 0.2.0

main.py

@@ -2,8 +2,10 @@
 
 Endpoints
 ---------
-- ``POST /api/{agent_name}/save``   — Save a memory
-- ``POST /api/{agent_name}/query``  — Query memories by semantic similarity
+- ``POST /api/{agent_name}/save``   — Save a memory (shared by default,
+                                       or private if ``private: true``)
+- ``POST /api/{agent_name}/query``  — Query memories visible to the agent
+                                       (all shared + its own private ones)
 - ``GET  /health``                   — Health check
 """
 
@@ -25,8 +27,9 @@ from store import MemoryStore
 app = FastAPI(
     title="Vector Memory Server",
     description="Semantic memory retrieval via REST. "
-    "Per-agent collections, powered by ChromaDB + all-MiniLM-L6-v2.",
-    version="0.1.0",
+    "Shared-by-default, private-opt-in. "
+    "ChromaDB + all-MiniLM-L6-v2.",
+    version="0.2.0",
 )
 
 store = MemoryStore(Config.DATA_DIR)
@@ -38,6 +41,7 @@ store = MemoryStore(Config.DATA_DIR)
 
 class SaveRequest(BaseModel):
     text: str
+    private: bool = False
     type: Optional[str] = "fact"
     tags: Optional[list[str]] = None
     date: Optional[str] = None
@@ -63,9 +67,15 @@ class QueryResponse(BaseModel):
 
 @app.post("/api/{agent_name}/save", response_model=SaveResponse)
 async def save_memory(agent_name: str, request: SaveRequest) -> SaveResponse:
-    """Embed and store a memory for the given agent."""
+    """Embed and store a memory for *agent_name*.
+
+    By default the memory is **shared** (visible to all agents).
+    Set ``private: true`` to restrict visibility to *agent_name* only.
+    """
     try:
-        metadata: dict = {}
+        metadata: dict = {
+            "private": request.private,
+        }
         if request.type:
             metadata["type"] = request.type
         if request.tags:
@@ -83,7 +93,11 @@ async def save_memory(agent_name: str, request: SaveRequest) -> SaveResponse:
 async def query_memory(
     agent_name: str, request: QueryRequest
 ) -> QueryResponse:
-    """Retrieve semantically similar memories for the given agent."""
+    """Retrieve memories visible to *agent_name*.
+
+    Returns all **shared** memories from any agent, plus **private**
+    memories owned by *agent_name*.
+    """
     try:
         results = store.query(agent_name, request.query, request.top_n)
         return QueryResponse(results=results)