feat(rag): harden post-LightRAG runtime

Retire legacy OCR/media/evidence fallbacks, add local-folder event bus and Page Aggregate guards, and archive completed design checklists.

Validation: cargo test -p mnote-web -- --test-threads=1; cargo test --workspace -- --test-threads=1; git diff --check; codegraph sync .; codegraph_status.

rust/crates/mnote-web/browser/sidebar-attachment-open-runtime.js

@@ -749,23 +749,7 @@ export const createSidebarAttachmentOpenRuntime = (dependencies = {}) => {
         };
       }
     }
-    if (assetId) {
-      var response = await fetch('/api/media/sign?assetId=' + encodeURIComponent(assetId), {
-        method: 'GET',
-        credentials: 'include',
-        cache: 'no-store'
-      });
-      var payload = await response.json().catch(function() { return null; });
-      if (!response.ok || !payload) {
-        throw new Error(payload && payload.error ? payload.error : '生成签名链接失败');
-      }
-      var signedUrl = String(payload && payload.signedUrl || '').trim();
-      if (!signedUrl) throw new Error('附件链接不可用');
-      return {
-        url: signedUrl,
-        asset: payload.asset && typeof payload.asset === 'object' ? payload.asset : {}
-      };
-    }
+    if (assetId) document.documentElement.setAttribute('data-mnote-media-sign-retired', 'true');
     var url = String(detail && (detail.fileUrl || detail.href) || '').trim();
     if (!url) throw new Error('附件链接不可用');
     return { url: url, asset: {} };
@@ -855,20 +839,7 @@ export const createSidebarAttachmentOpenRuntime = (dependencies = {}) => {
         return;
       }
     }
-    if (detail.assetId) {
-      try {
-        var response = await fetch('/api/media/sign?assetId=' + encodeURIComponent(detail.assetId), {
-          method: 'GET',
-          credentials: 'include'
-        });
-        var payload = await response.json().catch(function() { return null; });
-        var signedUrl = String(payload && payload.signedUrl || '').trim();
-        if (response.ok && signedUrl) {
-          window.open(signedUrl, '_blank', 'noopener,noreferrer');
-          return;
-        }
-      } catch (_) {}
-    }
+    if (detail.assetId) document.documentElement.setAttribute('data-mnote-media-sign-retired', 'true');
     var localRelativePath = String(detail.localRelativePath || '').trim();
     if (localRelativePath) {
       var localPathDownloadUrl = buildLocalFileOpenUrl(localRelativePath, true);