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>

apps/console/src/components/form/ControlMaturityLevelOptions.tsx

@@ -19,14 +19,11 @@ import {
 import { useTranslate } from "@probo/i18n";
 import { Option } from "@probo/ui";
 
-export const MATURITY_LEVEL_UNSET = "__unset__" as const;
-
 export function ControlMaturityLevelOptions() {
   const { __ } = useTranslate();
 
   return (
     <>
-      <Option value={MATURITY_LEVEL_UNSET}>{__("Not set")}</Option>
       {controlMaturityLevels.map(level => (
         <Option key={level} value={level}>
           {getControlMaturityLevelLabel(__, level)}