Remove unused config values

[ScriptSmith]

No description provided.

[greptile-apps]

Greptile Summary

This PR removes unused configuration values and their documentation to simplify the codebase and reduce maintenance burden.

Major changes:

• Removed unimplemented feature configs: vector_search, web_search, code_execution, moderation, prompt_caching, fallback, load_balancing
• Removed unused queue backends: RabbitMQ, SQS, Pub/Sub
• Removed unused cache TTL configs: daily_spend_secs, monthly_spend_secs
• Removed unused limits configs: token limits, budget exceeded actions
• Removed request logging config and related infrastructure
• Converted eviction_batch_size from config to constant with dynamic calculation
• Removed supports_streaming field from provider configs
• Updated documentation to reflect removed features

Minor behavioral changes:

• Memory cache eviction now uses dynamic batch size (10% of max_entries) instead of configured value
• X-XSS-Protection header default changed from "1; mode=block" to None (CSP provides protection)
• Tracing service name changed from "ai-gateway" to "hadrian"

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• Clean removal of unused code with thorough cleanup of all references. No remaining dependencies on removed config values were found. The few behavioral changes are minor and intentional improvements.
• No files require special attention

Important Files Changed

Filename	Overview
src/config/features.rs	Removed unused feature configs (vector_search, web_search, code_execution, moderation, prompt_caching, fallback, load_balancing) and queue backends (RabbitMq, Sqs, PubSub)
src/config/cache.rs	Removed eviction_batch_size, daily_spend_secs, and monthly_spend_secs from cache config
src/config/limits.rs	Removed token limits config and budget exceeded action/overage fields
src/config/observability.rs	Removed request_logging config and changed default tracing service name from 'ai-gateway' to 'hadrian'
src/config/ui.rs	Removed unused UI config options (gzip, brotli, history_enabled, max_conversations, code_execution, web_search, allowed_roles)
src/config/server.rs	Removed api_base_path and http2 config fields, changed X-XSS-Protection default from '1; mode=block' to None
src/cache/memory.rs	Converted eviction_batch_size from config to constant, updated eviction logic to use dynamic calculation (10% of max_entries)
src/app.rs	Removed fallback to vector_search.embedding config when initializing embedding service
src/init.rs	Removed fallback to vector_search.embedding in worker embedding service initialization
src/services/document_processor.rs	Removed RabbitMQ, SQS, and Pub/Sub queue backend implementations
src/config/providers.rs	Removed supports_streaming field from OpenAiProviderConfig, added comments about deny_unknown_fields constraints

_{Last reviewed commit: 148ee0e}