Scope sub-third-parties per parent

Replace the many-to-many junction table with a direct
parent_third_party_id foreign key on third_parties. Each
sub-third-party now belongs to exactly one parent, making
duplicates across parents independent entities.

Replace the firstLevel boolean with an integer level field
(1 = direct, 2+ = parent level + 1) to support arbitrary
nesting depth.

Remove the createThirdPartyThirdPartyMapping and
deleteThirdPartyThirdPartyMapping mutations, the CLI
link/unlink commands, and the corresponding MCP tools.
Creating a child third party now just requires passing
parentThirdPartyId on the existing createThirdParty mutation.

The frontend walks the parentThirdParty chain to build
display names like "Name (Ancestor1/Ancestor2)" and shows
clickable ancestor links on the detail page.

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

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

@@ -641,9 +641,9 @@ components:
         organization_id:
           $ref: "#/components/schemas/GID"
           description: Organization ID
-        first_level:
-          type: boolean
-          description: Filter by first-level status
+        level:
+          type: integer
+          description: Filter by level
         order_by:
           $ref: "#/components/schemas/ThirdPartyOrderBy"
           description: ThirdParty order by
@@ -667,38 +667,6 @@ components:
           items:
             $ref: "#/components/schemas/ThirdParty"
 
-    CreateThirdPartyThirdPartyMappingInput:
-      type: object
-      required:
-        - parent_third_party_id
-        - child_third_party_id
-      properties:
-        parent_third_party_id:
-          $ref: "#/components/schemas/GID"
-          description: Parent third party ID
-        child_third_party_id:
-          $ref: "#/components/schemas/GID"
-          description: Child third party ID
-
-    CreateThirdPartyThirdPartyMappingOutput:
-      type: object
-
-    DeleteThirdPartyThirdPartyMappingInput:
-      type: object
-      required:
-        - parent_third_party_id
-        - child_third_party_id
-      properties:
-        parent_third_party_id:
-          $ref: "#/components/schemas/GID"
-          description: Parent third party ID
-        child_third_party_id:
-          $ref: "#/components/schemas/GID"
-          description: Child third party ID
-
-    DeleteThirdPartyThirdPartyMappingOutput:
-      type: object
-
     ListChildThirdPartiesInput:
       type: object
       required:
@@ -737,7 +705,7 @@ components:
         - name
         - organization_id
         - category
-        - first_level
+        - level
         - created_at
         - updated_at
       properties:
@@ -861,9 +829,9 @@ components:
             - string
             - "null"
           description: Trust page URL
-        first_level:
-          type: boolean
-          description: Whether this is a first-level third party
+        level:
+          type: integer
+          description: Level of this third party (1 = direct, 2+ = indirect)
         created_at:
           type: string
           format: date-time
@@ -12055,22 +12023,6 @@ tools:
       $ref: "#/components/schemas/ListThirdPartiesInput"
     outputSchema:
       $ref: "#/components/schemas/ListThirdPartiesOutput"
-  - name: createThirdPartyThirdPartyMapping
-    description: Link a child third party to a parent third party
-    hints:
-      readonly: false
-    inputSchema:
-      $ref: "#/components/schemas/CreateThirdPartyThirdPartyMappingInput"
-    outputSchema:
-      $ref: "#/components/schemas/CreateThirdPartyThirdPartyMappingOutput"
-  - name: deleteThirdPartyThirdPartyMapping
-    description: Unlink a child third party from a parent third party
-    hints:
-      readonly: false
-    inputSchema:
-      $ref: "#/components/schemas/DeleteThirdPartyThirdPartyMappingInput"
-    outputSchema:
-      $ref: "#/components/schemas/DeleteThirdPartyThirdPartyMappingOutput"
   - name: listChildThirdParties
     description: List child third parties linked to a parent third party
     hints: