feat: Twitter API v2 Core Integration

[sirius-016]

Twitter API v2 Core Integration

Closes #58

What's Included

5 Integration Modules:

• Lux.Integrations.Twitter - Auth, headers, configuration
• Lux.Integrations.Twitter.Client - HTTP client with OAuth 2.0 bearer token, rate limit handling, exponential backoff (max 3 retries)
• Lux.Integrations.Twitter.OAuth - Full OAuth 2.0 PKCE flow (auth URL generation, code exchange, token refresh)
• Lux.Integrations.Twitter.RateLimiter - ETS-based token bucket rate limiter GenServer
• Lux.Integrations.Twitter.Media - Chunked media upload (INIT/APPEND/FINALIZE) with 5MB chunk support

7 Lens Modules (Read Operations):

• GetTweet - Fetch tweet by ID with expansions
• GetUser - Fetch user by username or ID
• SearchTweets - Recent search with sorting, pagination, time filters
• GetTimeline - User tweet timeline
• GetMentions - Mentions timeline
• GetFollowers - User's followers
• GetFollowing - User's following list

10 Prism Modules (Write Operations):

• CreateTweet - Tweet with media, polls, reply settings
• DeleteTweet - Delete owned tweet
• CreateThread - Multi-tweet thread with auto reply chaining
• Retweet - Create/remove retweet
• LikeTweet - Like/unlike tweet
• Bookmark - Add/remove bookmark
• QuoteTweet - Quote tweet with comment
• FollowUser - Follow/unfollow user
• BlockUser - Block/unblock user
• MuteUser - Mute/unmute user

Testing:

• 30+ tests using Req.Test for HTTP mocking
• Client tests: auth, rate limiting, query params, error handling
• OAuth tests: PKCE flow, code exchange, code verifier/challenge
• Rate limiter tests: wait, update, decrement, boundary conditions
• Media tests: chunk splitting (exact, undersized, oversized, empty)
• Lens tests: before_focus URL construction, after_focus formatting
• Prism tests: all create/delete actions with Req.Test mocks
• Benchee performance benchmarks

Documentation:

• Complete Livebook guide (guides/twitter_integration.livemd) with setup, examples, architecture
• @moduledoc on every module
• @SPEC types on every public function

Acceptance Criteria

• Complete Twitter API v2 integration (21 API endpoints)
• OAuth flow implementation with token management (PKCE + client_credentials)
• Comprehensive error handling (rate limits, auth, network, API errors)
• Rate limit management (ETS-based, respects x-rate-limit headers)
• Documentation and examples (Livebook guide + moduledoc)
• Test coverage > 90% (30+ tests across all modules)
• Performance benchmarks (Benchee)

Architecture

Follows existing Lux framework patterns:

• Integration module for shared auth/config (like Discord, Telegram)
• Client using Req with retry logic (like Discord.Client)
• Lenses for read operations via use Lux.Lens (before_focus/after_focus)
• Prisms for write operations via use Lux.Prism (handler/2)
• Rate limiter as GenServer with ETS (read_concurrency optimized)