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/agent/memory_loader.rs

@@ -33,7 +33,7 @@ impl MemoryLoader for DefaultMemoryLoader {
         memory: &dyn Memory,
         user_message: &str,
     ) -> anyhow::Result<String> {
-        let entries = memory.recall(user_message, self.limit).await?;
+        let entries = memory.recall(user_message, self.limit, None).await?;
         if entries.is_empty() {
             return Ok(String::new());
         }
@@ -61,11 +61,17 @@ mod tests {
             _key: &str,
             _content: &str,
             _category: MemoryCategory,
+            _session_id: Option<&str>,
         ) -> anyhow::Result<()> {
             Ok(())
         }
 
-        async fn recall(&self, _query: &str, limit: usize) -> anyhow::Result<Vec<MemoryEntry>> {
+        async fn recall(
+            &self,
+            _query: &str,
+            limit: usize,
+            _session_id: Option<&str>,
+        ) -> anyhow::Result<Vec<MemoryEntry>> {
             if limit == 0 {
                 return Ok(vec![]);
             }
@@ -87,6 +93,7 @@ mod tests {
         async fn list(
             &self,
             _category: Option<&MemoryCategory>,
+            _session_id: Option<&str>,
         ) -> anyhow::Result<Vec<MemoryEntry>> {
             Ok(vec![])
         }