Upgrade to FastAPI 0.124.0 with modern patterns

[alokemajumder]

Summary

Upgrades FastAPI to 0.124.0 and implements modern patterns for better documentation and type safety.

Dependencies Updated

Package	Old	New
FastAPI	0.115.4	0.124.0
Pydantic	2.9.2	2.10.3
Pydantic-settings	2.6.1	2.7.0
Uvicorn	0.32.0	0.32.1
Starlette	0.35.1	0.45.2
annotated-doc	-	0.1.0 (new)

New Features Implemented

Annotated Type Hints with Doc

• Dependencies use Annotated[Type, Doc("description")] for better OpenAPI docs
• Created typed dependency aliases: DatabaseSession, RequiredAPIKey, CurrentUser
• Enhanced parameter documentation in headers with examples

Enhanced Pydantic Models

• Added json_schema_extra with examples for all request/response models
• Implemented @computed_field for derived properties (is_complete, duration_seconds, total_pages)
• Added validation constraints (ge, le) to numeric fields
• Full Annotated[Type, Field(...), Doc(...)] pattern throughout

Improved OpenAPI Documentation

• Added tag descriptions for endpoint grouping
• Enhanced API description with markdown formatting (features, auth, rate limits)
• Configured Swagger UI parameters (deepLinking, persistAuthorization, displayRequestDuration)
• Added response schemas for error cases (400, 401, 429, 503)
• Enabled separate_input_output_schemas for cleaner schema generation

Code Quality

• Consistent use of status.HTTP_* constants
• Better error responses with structured ErrorResponse model
• Type hints throughout codebase

Files Changed

• requirements.txt - Updated core dependencies
• docker/requirements-stable.txt - Updated stable dependencies
• api/dependencies.py - Typed dependency aliases with Doc
• api/models/job.py - Enhanced Pydantic models with computed fields
• api/routers/convert.py - Modern endpoint definitions with response schemas
• api/main.py - Enhanced OpenAPI configuration

Test Plan

• Docker compose config validates
• Swagger UI loads with enhanced documentation
• API endpoints respond correctly
• Type hints work with IDE autocomplete