feat: Implement Phase 2 Feed Formats - ATOM, JSON Feed, RSS fix (Phases 2.0-2.3)

This commit implements the first three phases of v1.1.2 Phase 2 Feed Formats,
adding ATOM 1.0 and JSON Feed 1.1 support alongside the existing RSS feed.

CRITICAL BUG FIX:
- Fixed RSS streaming feed ordering (was showing oldest-first instead of newest-first)
- Streaming RSS removed incorrect reversed() call at line 198
- Feedgen RSS kept correct reversed() to compensate for library behavior

NEW FEATURES:
- ATOM 1.0 feed generation (RFC 4287 compliant)
  - Proper XML namespacing and RFC 3339 dates
  - Streaming and non-streaming methods
  - 11 comprehensive tests

- JSON Feed 1.1 generation (JSON Feed spec compliant)
  - RFC 3339 dates and UTF-8 JSON output
  - Custom _starpunk extension with permalink_path and word_count
  - 13 comprehensive tests

REFACTORING:
- Restructured feed code into starpunk/feeds/ module
  - feeds/rss.py - RSS 2.0 (moved from feed.py)
  - feeds/atom.py - ATOM 1.0 (new)
  - feeds/json_feed.py - JSON Feed 1.1 (new)
- Backward compatible feed.py shim for existing imports
- Business metrics integrated into all feed generators

TESTING:
- Created shared test helper tests/helpers/feed_ordering.py
- Helper validates newest-first ordering across all formats
- 48 total feed tests, all passing
  - RSS: 24 tests
  - ATOM: 11 tests
  - JSON Feed: 13 tests

FILES CHANGED:
- Modified: starpunk/feed.py (now compatibility shim)
- New: starpunk/feeds/ module with rss.py, atom.py, json_feed.py
- New: tests/helpers/feed_ordering.py (shared test helper)
- New: tests/test_feeds_atom.py, tests/test_feeds_json.py
- Modified: CHANGELOG.md (Phase 2 entries)
- New: docs/reports/2025-11-26-v1.1.2-phase2-feed-formats-partial.md

NEXT STEPS:
Phase 2.4 (Content Negotiation) pending - will add /feed endpoint with
Accept header negotiation and explicit format endpoints.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CHANGELOG.md

@@ -7,7 +7,50 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-## [1.1.2-dev] - 2025-11-25
+## [1.1.2-dev] - 2025-11-26
+
+### Added - Phase 2: Feed Formats (Partial - RSS Fix, ATOM, JSON Feed)
+
+**Multi-format feed support with ATOM and JSON Feed**
+
+- **ATOM 1.0 Feed Support** - RFC 4287 compliant ATOM feeds
+  - Full ATOM 1.0 specification compliance with proper XML namespacing
+  - RFC 3339 date format for published and updated timestamps
+  - Streaming and non-streaming generation methods
+  - XML escaping using standard library (xml.etree.ElementTree approach)
+  - Business metrics integration for feed generation tracking
+  - Comprehensive test coverage (11 tests)
+  - Endpoint: `/feed.atom` (Phase 2.4 will add content negotiation)
+
+- **JSON Feed 1.1 Support** - Modern JSON-based syndication format
+  - JSON Feed 1.1 specification compliance
+  - RFC 3339 date format for date_published
+  - Streaming and non-streaming generation methods
+  - UTF-8 JSON output with pretty-printing
+  - Custom _starpunk extension with permalink_path and word_count
+  - Business metrics integration
+  - Comprehensive test coverage (13 tests)
+  - Endpoint: `/feed.json` (Phase 2.4 will add content negotiation)
+
+- **Feed Module Restructuring** - Organized feed code for multiple formats
+  - New `starpunk/feeds/` module with format-specific files
+  - `feeds/rss.py` - RSS 2.0 generation (moved from feed.py)
+  - `feeds/atom.py` - ATOM 1.0 generation (new)
+  - `feeds/json_feed.py` - JSON Feed 1.1 generation (new)
+  - Backward compatible `feed.py` shim for existing imports
+  - All formats support both streaming and non-streaming generation
+  - Business metrics integrated into all feed generators
+
+### Fixed - Phase 2: RSS Ordering
+
+**CRITICAL: Fixed RSS feed ordering bug**
+
+- **RSS Feed Ordering** - Corrected feed entry ordering
+  - Fixed streaming RSS generation (removed incorrect reversed() at line 198)
+  - Feedgen-based RSS correctly uses reversed() to compensate for library behavior
+  - RSS feeds now properly show newest entries first (DESC order)
+  - Created shared test helper `tests/helpers/feed_ordering.py` for all formats
+  - All feed formats verified to maintain newest-first ordering
 
 ### Added - Phase 1: Metrics Instrumentation