[LLM] Create LLM feature documentation

[Johnpii1]

Description

Description
Add LLMFeedback ORM model to persist feature, prompt, output, rating, expert flag/weight and timestamps (api/models/orm.py).
Add LLM feedback request/response schemas and dashboard/prompt-improvement models (api/schemas.py) and validate inputs (LLMFeedbackIn / LLMFeedbackOut).
Expose feedback APIs on the LLM router: POST /api/v1/llm/feedback, GET /api/v1/llm/feedback/dashboard, and GET /api/v1/llm/feedback/prompt-improvements with aggregation/weighted metrics (api/routers/llm.py).
Add deterministic LLM mocking helpers with latency, token/cost accounting and injectable failures for chaos testing (api/tests/llm_mocking.py).
Add golden regression cases and an integration test suite that enforces p95 latency gate, mock-cost gates, chaos behavior and feedback/dashboard flows (api/tests/llm_golden/ask_cases.json, api/tests/test_llm_integration_quality.py).
Document public LLM endpoints, usage examples, testing guidance and troubleshooting in docs/llm/features.md.

Testing
Successfully compiled the modified modules with python -m py_compile api/routers/llm.py api/routers/feedback.py api/models/orm.py api/schemas.py api/tests/test_llm_integration_quality.py api/tests/llm_mocking.py and no syntax errors were reported.
Ran pytest ... invocation for the LLM integration tests but it was blocked by missing dependency fastapi (test collection failed with ModuleNotFoundError: No module named 'fastapi'), so the full pytest suite could not be executed in the current environment.
Unit-level sanity checks (file compilation) passed; the new integration tests and endpoints are present and ready to run in CI or a dev environment with required dependencies installed.

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context.

Fixes # (issue)
close #403

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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