fix(models): use enum values instead of names for PostgreSQL

Add values_callable to all enum columns so SQLAlchemy serializes using
the enum's .value (lowercase) instead of .name (uppercase). PostgreSQL
enum types defined in migrations use lowercase values.

Fixes: invalid input value for enum autonomy_level: "MILESTONE"

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

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

backend/app/models/syndarix/project.py

@@ -35,28 +35,44 @@ class Project(Base, UUIDMixin, TimestampMixin):
     description = Column(Text, nullable=True)
 
     autonomy_level: Column[AutonomyLevel] = Column(
-        Enum(AutonomyLevel, name="autonomy_level"),
+        Enum(
+            AutonomyLevel,
+            name="autonomy_level",
+            values_callable=lambda x: [e.value for e in x],
+        ),
         default=AutonomyLevel.MILESTONE,
         nullable=False,
         index=True,
     )
 
     status: Column[ProjectStatus] = Column(
-        Enum(ProjectStatus, name="project_status"),
+        Enum(
+            ProjectStatus,
+            name="project_status",
+            values_callable=lambda x: [e.value for e in x],
+        ),
         default=ProjectStatus.ACTIVE,
         nullable=False,
         index=True,
     )
 
     complexity: Column[ProjectComplexity] = Column(
-        Enum(ProjectComplexity, name="project_complexity"),
+        Enum(
+            ProjectComplexity,
+            name="project_complexity",
+            values_callable=lambda x: [e.value for e in x],
+        ),
         default=ProjectComplexity.MEDIUM,
         nullable=False,
         index=True,
     )
 
     client_mode: Column[ClientMode] = Column(
-        Enum(ClientMode, name="client_mode"),
+        Enum(
+            ClientMode,
+            name="client_mode",
+            values_callable=lambda x: [e.value for e in x],
+        ),
         default=ClientMode.AUTO,
         nullable=False,
         index=True,