Replace implemented column with CMMI maturity level

Drop the boolean implemented/not-implemented state in favor of a
mandatory CMMI maturity level enum (NONE, INITIAL, MANAGED, DEFINED,
QUANTITATIVELY_MANAGED, OPTIMIZING) stored as a Postgres enum type.

The migration backfills existing rows (NOT_IMPLEMENTED → NONE,
IMPLEMENTED → INITIAL), makes the column NOT NULL, and drops the old
implemented column and its enum type.

- maturityLevel is required on CreateControlInput and non-nullable (!)
  in the GraphQL schema
- CLI displays human-readable CMMI labels instead of raw enum tokens
- SOA table and published document use a single Maturity column in
  place of the old Implemented + Maturity columns
- Remove ControlImplementationState type and all implemented references
  across backend, frontend, CLI, MCP, n8n, and E2E tests

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/coredata/migrations/20260419T172808Z.sql

@@ -12,4 +12,25 @@
 -- OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 -- PERFORMANCE OF THIS SOFTWARE.
 
-ALTER TABLE controls ADD COLUMN maturity_level TEXT;
+CREATE TYPE control_maturity_level AS ENUM (
+    'NONE',
+    'INITIAL',
+    'MANAGED',
+    'DEFINED',
+    'QUANTITATIVELY_MANAGED',
+    'OPTIMIZING'
+);
+
+ALTER TABLE controls ADD COLUMN maturity_level control_maturity_level;
+
+UPDATE controls SET maturity_level = CASE
+    WHEN implemented = 'NOT_IMPLEMENTED' THEN 'NONE'::control_maturity_level
+    ELSE 'INITIAL'::control_maturity_level
+END;
+
+ALTER TABLE controls ALTER COLUMN maturity_level SET NOT NULL;
+ALTER TABLE controls ALTER COLUMN implemented DROP NOT NULL;
+
+-- TODO: drop column and type in a future migration
+-- ALTER TABLE controls DROP COLUMN implemented;
+-- DROP TYPE control_implementation_state;