收口 MNote P0 P1 P2 审查尾项

- 归档 OnlyOffice live bridge、Page AI、mindmap、design governance 与相关 bug 条目
- 补齐 MinerU OCR 后端 runtime 合同与 smoke/test 基线
- 收口 ChatOnly/Doubao、ObjectIdentity、Page Aggregate compat 与 runtime owner 文档口径

验证：
- cargo test --manifest-path rust/Cargo.toml -p mnote-web local_ocr -- --test-threads=1
- cargo test --manifest-path rust/Cargo.toml -p mnote-web onlyoffice_bridge -- --test-threads=1
- git diff --check
- git diff --cached --check
- codegraph index . --force && codegraph status .
- codegraph sync . && codegraph status .

rust/crates/mnote-web/src/page_aggregate/builder.rs

@@ -65,7 +65,7 @@ impl PageAggregateBuilder {
         Self {
             document_id: String::new(),
             workspace_id: "default".to_string(),
-            source: PageAggregateSource::CompatMetaContentJoin,
+            source: PageAggregateSource::KernelProjection,
             parent_id: None,
             path: Vec::new(),
             sidebar_tree_membership: vec!["page-tree".into(), "file-tree".into()],
@@ -372,3 +372,29 @@ impl Default for PageAggregateBuilder {
         Self::new()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn new_defaults_to_kernel_projection() {
+        let aggregate = PageAggregateBuilder::new()
+            .document_id("doc_1")
+            .workspace_id("ws_demo")
+            .build();
+
+        assert_eq!(aggregate.source, PageAggregateSource::KernelProjection);
+    }
+
+    #[test]
+    fn explicit_compat_source_is_still_supported() {
+        let aggregate = PageAggregateBuilder::new()
+            .document_id("doc_1")
+            .workspace_id("ws_demo")
+            .source(PageAggregateSource::CompatMetaContentJoin)
+            .build();
+
+        assert_eq!(aggregate.source, PageAggregateSource::CompatMetaContentJoin);
+    }
+}