feat(dream): add skill ownership guard with dream_managed frontmatter

- Dream-created skills get  in SKILL.md frontmatter
-  tags each skill as [dream]/[user]/[builtin]
- New config  (default False): when False Dream
  can only modify [dream] skills; when True [user] skills are also editable
- [builtin] skills are never editable
- dream.md prompt uses Jinja conditional to render edit policy
- WebUI types and test fixtures updated with new config field

webui/src/lib/types.ts

@@ -265,6 +265,7 @@ export interface SettingsPayload {
       max_batch_size: number;
       max_iterations: number;
       annotate_line_ages: boolean;
+      dream_edit_user_skills: boolean;
     };
     unified_session: boolean;
   };

webui/src/tests/app-layout.test.tsx

@@ -92,6 +92,7 @@ function baseSettingsPayload() {
         max_batch_size: 20,
         max_iterations: 15,
         annotate_line_ages: true,
+        dream_edit_user_skills: false,
       },
       unified_session: false,
     },
@@ -780,6 +781,7 @@ describe("App layout", () => {
                   max_batch_size: 20,
                   max_iterations: 15,
                   annotate_line_ages: true,
+        dream_edit_user_skills: false,
                 },
                 unified_session: false,
               },
@@ -1066,6 +1068,7 @@ describe("App layout", () => {
                   max_batch_size: 20,
                   max_iterations: 15,
                   annotate_line_ages: true,
+        dream_edit_user_skills: false,
                 },
                 unified_session: false,
               },