Fix session executor storage to only store base executor name (Vibe Kanban) (#1621)

* The code compiles successfully. Let me provide a summary of what was done:

## Summary

I've implemented the fix for the session executor storage format issue:

### Changes Made

1. **`crates/services/src/services/container.rs` (line 912)**
   - Changed `executor_profile_id.to_string()` to `executor_profile_id.executor.to_string()`
   - This now stores only the base executor name (e.g., `"CLAUDE_CODE"`) instead of the full format with variant (e.g., `"CLAUDE_CODE:ROUTER"`)

2. **`crates/db/migrations/20251220134608_fix_session_executor_format.sql`**
   - Added migration to fix existing erroneous entries
   - Strips the variant suffix from any executor values containing a colon
   - Excludes valid hyphenated values like `dev-server`, `setup-script`, etc.

The fix compiles successfully. This will restore the expected behavior for:
- Capability lookups in `UserMessage.tsx`
- Default profile selection in `CreateAttemptDialog.tsx`

* Simplified. The `LIKE '%:%'` condition is sufficient - it only matches values containing a colon, which are exactly the erroneous `"EXECUTOR:VARIANT"` format entries we need to fix.

crates/services/src/services/container.rs

@@ -909,7 +909,7 @@ pub trait ContainerService {
         let session = Session::create(
             &self.db().pool,
             &CreateSession {
-                executor: Some(executor_profile_id.to_string()),
+                executor: Some(executor_profile_id.executor.to_string()),
             },
             Uuid::new_v4(),
             workspace.id,