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/server/api/mcp/v1/specification.yaml

@@ -4212,7 +4212,7 @@ components:
         - section_title
         - name
         - best_practice
-        - implemented
+        - maturity_level
         - created_at
         - updated_at
       properties:
@@ -4239,23 +4239,16 @@ components:
         best_practice:
           type: boolean
           description: Whether control is a best practice
-        implemented:
+        maturity_level:
           type: string
-          enum: [IMPLEMENTED, NOT_IMPLEMENTED]
-          description: Control implementation state
-          go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.ControlImplementationState
+          enum: [NONE, INITIAL, MANAGED, DEFINED, QUANTITATIVELY_MANAGED, OPTIMIZING]
+          description: CMMI 0-5 maturity level of the control
+          go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.ControlMaturityLevel
         not_implemented_justification:
           type:
             - string
             - "null"
           description: Justification for non-implementation
-        maturity_level:
-          type:
-            - string
-            - "null"
-          enum: [NONE, INITIAL, MANAGED, DEFINED, QUANTITATIVELY_MANAGED, OPTIMIZING, null]
-          description: CMMI 0-5 maturity level of the control
-          go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.ControlMaturityLevel
         created_at:
           type: string
           format: date-time
@@ -4330,7 +4323,7 @@ components:
         - section_title
         - name
         - best_practice
-        - implemented
+        - maturity_level
       properties:
         organization_id:
           $ref: "#/components/schemas/GID"
@@ -4350,23 +4343,16 @@ components:
         best_practice:
           type: boolean
           description: Whether control is a best practice
-        implemented:
+        maturity_level:
           type: string
-          enum: [IMPLEMENTED, NOT_IMPLEMENTED]
-          description: Control implementation state
-          go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.ControlImplementationState
+          enum: [NONE, INITIAL, MANAGED, DEFINED, QUANTITATIVELY_MANAGED, OPTIMIZING]
+          description: CMMI 0-5 maturity level of the control
+          go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.ControlMaturityLevel
         not_implemented_justification:
           type:
             - string
             - "null"
           description: Justification for non-implementation
-        maturity_level:
-          type:
-            - string
-            - "null"
-          enum: [NONE, INITIAL, MANAGED, DEFINED, QUANTITATIVELY_MANAGED, OPTIMIZING, null]
-          description: CMMI 0-5 maturity level of the control
-          go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.ControlMaturityLevel
 
     AddControlOutput:
       type: object
@@ -4397,21 +4383,15 @@ components:
         best_practice:
           type: boolean
           description: Whether control is a best practice
-        implemented:
+        maturity_level:
           type: string
-          enum: [IMPLEMENTED, NOT_IMPLEMENTED]
-          description: Control implementation state
-          go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.ControlImplementationState
+          enum: [NONE, INITIAL, MANAGED, DEFINED, QUANTITATIVELY_MANAGED, OPTIMIZING]
+          description: CMMI 0-5 maturity level of the control
+          go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.ControlMaturityLevel
         not_implemented_justification:
           type: ["string", "null"]
           description: Justification for non-implementation
           go.probo.inc/mcpgen/omittable: true
-        maturity_level:
-          type: ["string", "null"]
-          enum: [NONE, INITIAL, MANAGED, DEFINED, QUANTITATIVELY_MANAGED, OPTIMIZING, null]
-          description: CMMI 0-5 maturity level of the control
-          go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.ControlMaturityLevel
-          go.probo.inc/mcpgen/omittable: true
 
     UpdateControlOutput:
       type: object