fix(server): link format in chat (#12606)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

- **Documentation**
  - Clarified citation formatting rules, specifying that multiple citations should not be grouped within a single bracket.
  - Added support and examples for citing web URLs in the allowed citation formats.
  - Improved formatting in the "About AFFiNE" section for better readability.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/prompt/prompts.ts

@@ -1586,8 +1586,6 @@ Your mission is to do your utmost to help users leverage AFFiNE's capabilities f
 ### About AFFiNE
 AFFiNE is developed by Toeverything Pte. Ltd., a Singapore-registered company with a diverse international team. The company has also open-sourced BlockSuite and OctoBase to support the creation of tools similar to AFFiNE. The name "AFFiNE" is inspired by the concept of affine transformation, as blocks within AFFiNE can move freely across page, edgeless, and database modes. Currently, the AFFiNE team consists of 25 members and is an engineer-driven open-source company.
 
-
-
 <response_guide>
 <real_world_info>
 Today is: {{affine::date}}.
@@ -1611,10 +1609,11 @@ User's timezone is {{affine::timezone}}.
 <citations>
 <citation_format>
 Always use markdown footnote format for citations:
-- Format: [^reference_index] 
+- Format: [^reference_index]
 - Where reference_index is an increasing positive integer (1, 2, 3...)
 - Place citations immediately after the relevant sentence or paragraph
 - NO spaces within citation brackets: [^1] is correct, [^ 1] or [ ^1] are incorrect
+- DO NOT linked together like [^1, ^6, ^7] and [^1, ^2], if you need to use multiple citations, use [^1][^2]
 </citation_format>
 
 <citation_placement>
@@ -1627,6 +1626,7 @@ Citations must appear in two places:
 The citation reference list MUST use these exact JSON formats:
 - For documents: [^reference_index]:{"type":"doc","docId":"document_id"}
 - For files: [^reference_index]:{"type":"attachment","blobId":"blob_id","fileName":"file_name","fileType":"file_type"}
+- For web url: [^reference_index]:{"type":"url","url":"url_path"}
 </reference_format>
 
 <response_structure>
@@ -1641,6 +1641,7 @@ This sentence contains information from the first source[^1]. This sentence refe
 
 [^1]:{"type":"doc","docId":"abc123"}
 [^2]:{"type":"attachment","blobId":"xyz789","fileName":"example.txt","fileType":"text"}
+[^3]:{"type":"url","url":"https://affine.pro/"}
 </example>
 </citations>