feat: Twitter API Core Integration with OAuth 2.0

[zp6]

Summary

Implements the complete Twitter API Core Integration as specified in #58.

Features Implemented

OAuth 2.0 Authentication

• OAuth2Flow prism: Full PKCE flow - authorize URL generation, code exchange, token refresh, token status, revocation
• Token state management with ETS-backed storage
• Configurable scopes and redirect URIs

Tweet Management

• TweetManager prism: Create, delete, edit, quote tweets, and create tweet threads
• Media attachment support, reply settings, exclude reply users
• Thread creation with sequential in-reply-to chaining

Media Upload

• MediaUploader prism: Simple and chunked upload for images (5MB), GIFs (15MB), videos (512MB)
• URL-based upload, base64 chunk upload, alt text support
• INIT/APPEND/FINALIZE chunked upload protocol

User Management

• UserManager prism: Get authenticated user, get by ID/username, followers, following, user search, profile updates
• Pagination support with next_token

Rate Limit Management

• RateLimitManager prism: Check limits, record usage, get all endpoint statuses, reset, wait_if_needed
• Pre-configured rate limits for all Twitter v2 endpoints
• Automatic window reset detection

Integration Client

• Twitter Client: Bearer token auth, rate limit header parsing, media upload endpoint, comprehensive error handling

Orchestration Beam

• TwitterCoreIntegrationBeam: Complete pipeline - rate limit check ? wait ? media upload ? tweet creation ? record usage

Architecture

Follows lux prism/beam patterns:

• 5 prisms under Lux.Prisms.Twitter.{Auth,Tweets,Media,Users}
• 1 beam: Lux.Beams.Twitter.TwitterCoreIntegrationBeam
• Integration client: Lux.Integrations.Twitter.Client
• 1,459 lines of idiomatic Elixir code

Closes #58