[feat][backend]: add chat view and thread query

[kidkidkid]

• Add GetTraceChat/GetThreadChat/GetThreadStat IDL definitions
• Add ChatMessage struct with message_type and span fields
• Implement ChatProcessor for extracting last user message from model span input
• Support Standard ChatCompletion and Responses API formats
• Add service layer implementations with chat processor integration
• Add application handler layer with permission validation
• Add ChatMessagesDO2DTO convertor function
• Add unit tests for ChatProcessor

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• This PR title match the format: [<type>][<scope>] <description>. For example: [fix][backend] flaky fix
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[codecov]

Codecov Report

❌ Patch coverage is 87.11790% with 59 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...bservability/domain/trace/service/trace_service.go	88.66%	19 Missing and 9 partials ⚠️
...ace/service/trace/span_processor/chat_processor.go	87.50%	5 Missing and 3 partials ⚠️
backend/modules/observability/application/trace.go	93.69%	4 Missing and 3 partials ⚠️
...ckend/modules/observability/infra/repo/ck/spans.go	0.00%	6 Missing and 1 partial ⚠️
...dler/coze/loop/apis/observability_trace_service.go	0.00%	6 Missing ⚠️
backend/modules/observability/infra/repo/trace.go	66.66%	2 Missing and 1 partial ⚠️

@@            Coverage Diff             @@
##             main     #475      +/-   ##
==========================================
+ Coverage   75.70%   75.78%   +0.08%     
==========================================
  Files         642      643       +1     
  Lines       68902    69355     +453     
==========================================
+ Hits        52162    52563     +401     
- Misses      13465    13503      +38     
- Partials     3275     3289      +14     

Flag	Coverage Δ
unittests	75.78% <87.11%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...observability/application/convertor/trace/trace.go	59.45% <100.00%> (+19.45%)	⬆️
...bservability/domain/trace/entity/loop_span/span.go	80.31% <100.00%> (+0.06%)	⬆️
backend/modules/observability/infra/repo/trace.go	84.77% <66.66%> (-0.30%)	⬇️
...dler/coze/loop/apis/observability_trace_service.go	0.00% <0.00%> (ø)
backend/modules/observability/application/trace.go	75.13% <93.69%> (+2.43%)	⬆️
...ckend/modules/observability/infra/repo/ck/spans.go	74.28% <0.00%> (-1.17%)	⬇️
...ace/service/trace/span_processor/chat_processor.go	87.50% <87.50%> (ø)
...bservability/domain/trace/service/trace_service.go	87.29% <88.66%> (+0.21%)	⬆️

... and 2 files with indirect coverage changes

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