[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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[codecov]

Codecov Report

❌ Patch coverage is 86.61710% with 72 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...bservability/domain/trace/service/trace_service.go	88.43%	25 Missing and 9 partials ⚠️
...ace/service/trace/span_processor/chat_processor.go	85.89%	8 Missing and 3 partials ⚠️
backend/modules/observability/application/trace.go	92.18%	7 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	60.00%	3 Missing and 1 partial ⚠️

@@            Coverage Diff             @@
##             main     #475      +/-   ##
==========================================
- Coverage   77.06%   76.08%   -0.98%     
==========================================
  Files         649      650       +1     
  Lines       72033    87461   +15428     
==========================================
+ Hits        55513    66548   +11035     
- Misses      13200    17574    +4374     
- Partials     3320     3339      +19     

Flag	Coverage Δ
unittests	76.08% <86.61%> (-0.98%)	⬇️

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	57.14% <100.00%> (+17.14%)	⬆️
...bservability/domain/trace/entity/loop_span/span.go	81.14% <100.00%> (-2.09%)	⬇️
backend/modules/observability/infra/repo/trace.go	82.08% <60.00%> (-3.84%)	⬇️
...dler/coze/loop/apis/observability_trace_service.go	0.00% <0.00%> (ø)
...ckend/modules/observability/infra/repo/ck/spans.go	70.95% <0.00%> (-4.50%)	⬇️
backend/modules/observability/application/trace.go	74.56% <92.18%> (-0.05%)	⬇️
...ace/service/trace/span_processor/chat_processor.go	85.89% <85.89%> (ø)
...bservability/domain/trace/service/trace_service.go	87.06% <88.43%> (-1.64%)	⬇️

... and 579 files with indirect coverage changes

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