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/docgen/generator.go

@@ -289,9 +289,8 @@ type (
 		ControlName          string
 		Applicability        string
 		Justification        string
-		Implemented          string
-		NotImplJustification string
 		MaturityLevel        string
+		NotImplJustification string
 		Regulatory           string
 		Contractual          string
 		BestPractice         string
@@ -321,11 +320,8 @@ func BoolLabel(v bool) string {
 	return "No"
 }
 
-func MaturityLabel(l *coredata.ControlMaturityLevel) string {
-	if l == nil {
-		return "Not set"
-	}
-	switch *l {
+func MaturityLabel(l coredata.ControlMaturityLevel) string {
+	switch l {
 	case coredata.ControlMaturityLevelNone:
 		return "0 - None"
 	case coredata.ControlMaturityLevelInitial: