feat(memory): add session_id isolation to Memory trait (#530)

* feat(memory): add session_id isolation to Memory trait

Add optional session_id parameter to store(), recall(), and list()
methods across the Memory trait and all four backends (sqlite, markdown,
lucid, none). This enables per-session memory isolation so different
agent sessions cannot cross-read each other's stored memories.

Changes:
- traits.rs: Add session_id: Option<&str> to store/recall/list
- sqlite.rs: Schema migration (ALTER TABLE ADD COLUMN session_id),
  index, persist/filter by session_id in all query paths
- markdown.rs, lucid.rs, none.rs: Updated signatures
- All callers pass None for backward compatibility
- 5 new tests: session-filtered recall, cross-session isolation,
  session-filtered list, no-filter returns all, migration idempotency

Closes #518

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

* fix(channels): fix discord _channel_id typo and lark missing reply_to

Pre-existing compilation errors on main after reply_to was added to
ChannelMessage: discord.rs used _channel_id (underscore prefix) but
referenced channel_id, and lark.rs was missing the reply_to field.

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

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/memory/traits.rs

@@ -44,18 +44,32 @@ pub trait Memory: Send + Sync {
     /// Backend name
     fn name(&self) -> &str;
 
-    /// Store a memory entry
-    async fn store(&self, key: &str, content: &str, category: MemoryCategory)
-        -> anyhow::Result<()>;
+    /// Store a memory entry, optionally scoped to a session
+    async fn store(
+        &self,
+        key: &str,
+        content: &str,
+        category: MemoryCategory,
+        session_id: Option<&str>,
+    ) -> anyhow::Result<()>;
 
-    /// Recall memories matching a query (keyword search)
-    async fn recall(&self, query: &str, limit: usize) -> anyhow::Result<Vec<MemoryEntry>>;
+    /// Recall memories matching a query (keyword search), optionally scoped to a session
+    async fn recall(
+        &self,
+        query: &str,
+        limit: usize,
+        session_id: Option<&str>,
+    ) -> anyhow::Result<Vec<MemoryEntry>>;
 
     /// Get a specific memory by key
     async fn get(&self, key: &str) -> anyhow::Result<Option<MemoryEntry>>;
 
-    /// List all memory keys, optionally filtered by category
-    async fn list(&self, category: Option<&MemoryCategory>) -> anyhow::Result<Vec<MemoryEntry>>;
+    /// List all memory keys, optionally filtered by category and/or session
+    async fn list(
+        &self,
+        category: Option<&MemoryCategory>,
+        session_id: Option<&str>,
+    ) -> anyhow::Result<Vec<MemoryEntry>>;
 
     /// Remove a memory by key
     async fn forget(&self, key: &str) -> anyhow::Result<bool>;