fix(memory): unify Outcome enum and add ABANDONED support

- Add ABANDONED value to core Outcome enum in types.py
- Replace duplicate OutcomeType class in mcp/tools.py with alias to Outcome
- Simplify mcp/service.py to use outcome directly (no more silent mapping)
- Add migration 0006 to extend PostgreSQL episode_outcome enum
- Add missing constraints to migration 0005 (ix_facts_unique_triple_global)

This fixes the semantic issue where ABANDONED outcomes were silently
converted to FAILURE, losing information about task abandonment.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/services/memory/mcp/service.py

@@ -1024,15 +1024,8 @@ class MemoryToolService:
         context: ToolContext,
     ) -> dict[str, Any]:
         """Execute the 'record_outcome' tool."""
-        # Map outcome type to memory Outcome
-        # Note: ABANDONED maps to FAILURE since core Outcome doesn't have ABANDONED
-        outcome_map = {
-            OutcomeType.SUCCESS: Outcome.SUCCESS,
-            OutcomeType.PARTIAL: Outcome.PARTIAL,
-            OutcomeType.FAILURE: Outcome.FAILURE,
-            OutcomeType.ABANDONED: Outcome.FAILURE,  # No ABANDONED in core enum
-        }
-        outcome = outcome_map.get(args.outcome, Outcome.FAILURE)
+        # OutcomeType is now an alias for Outcome, use directly
+        outcome = args.outcome
 
         # Record in episodic memory
         episodic = await self._get_episodic()