feat(business): implement block-based content editing and rich text rendering

Introduce a new `BlockEditor` component and upgrade the post/message
rendering system to support rich text segments (images, @mentions,
votes, and post references).

- Implement `BlockEditor` for long-form post creation with image
  embedding support.
- Upgrade `PostContentRenderer` and `SegmentRenderer` to handle
  complex segment types including inline images and block elements.
- Refactor `PostCard` to use segment-based content and image
  signatures for optimized memoization.
- Centralize segment partitioning logic in `segmentUtils.ts` to ensure
  consistent rendering across chat and post modules.
- Update `PostRepository` and `Post` entity to support the new
  `segments` data structure.

src/types/dto/segmentUtils.ts

@@ -1,10 +1,65 @@
 /**
- * Segment text extraction utilities
+ * Segment utilities
  */
 
 import type { MessageSegment, TextSegmentData, AtSegmentData, FileSegmentData, FaceSegmentData, LinkSegmentData, PostRefSegmentData } from './message';
 import type { UserDTO } from './user';
 
+// ==================== Chunk Types ====================
+
+export type ContentChunk =
+  | { kind: 'inline'; parts: MessageSegment[] }
+  | { kind: 'images'; parts: MessageSegment[] }
+  | { kind: 'block'; segment: MessageSegment };
+
+/**
+ * 将 segments 分成三种 chunk：
+ * - inline: text / at / face 等行内元素
+ * - images: 连续的图片 segment 组合
+ * - block:  vote / post_ref / video / file / link / voice 等块级元素
+ *
+ * 与聊天和帖子详情共用同一套分组逻辑。
+ */
+export function partitionSegments(segments: MessageSegment[]): ContentChunk[] {
+  const out: ContentChunk[] = [];
+  let inlineBuf: MessageSegment[] = [];
+  const flushInline = () => {
+    if (inlineBuf.length) {
+      out.push({ kind: 'inline', parts: [...inlineBuf] });
+      inlineBuf = [];
+    }
+  };
+
+  for (const s of segments) {
+    if (s.type === 'image') {
+      flushInline();
+      const last = out[out.length - 1];
+      if (last?.kind === 'images') {
+        last.parts.push(s);
+      } else {
+        out.push({ kind: 'images', parts: [s] });
+      }
+    } else if (
+      s.type === 'vote' ||
+      s.type === 'post_ref' ||
+      s.type === 'video' ||
+      s.type === 'file' ||
+      s.type === 'link' ||
+      s.type === 'voice'
+    ) {
+      flushInline();
+      out.push({ kind: 'block', segment: s });
+    } else if (s.type === 'text' || s.type === 'at' || s.type === 'face') {
+      inlineBuf.push(s);
+    } else {
+      // 未知类型也当作 inline 处理，避免丢失内容
+      inlineBuf.push(s);
+    }
+  }
+  flushInline();
+  return out;
+}
+
 /**
  * Extract plain text from message segments for display
  */