fix: Add trailing slash to SITE_URL and enhance debug logging (v0.9.1)

Fix 1: SITE_URL trailing slash normalization
- IndieLogin.com requires client_id URLs to have trailing slash for root domains
- Added automatic normalization in load_config() after env loading
- Added secondary normalization after config overrides (for test compatibility)
- Fixes "client_id is not registered" authentication errors
- Updated redirect_uri construction to avoid double slashes

Fix 2: Enhanced httpx debug logging
- Added detailed request logging before token exchange POST
- Added detailed response logging after token exchange POST
- Shows exact HTTP method, URL, headers, and body for troubleshooting
- All sensitive data (tokens, verifiers) automatically redacted
- Supplements existing _log_http_request/_log_http_response helpers

Version: 0.9.1 (PATCH - bug fixes)
- Updated __version__ in starpunk/__init__.py
- Added CHANGELOG entry for v0.9.1

Tests: 486/514 passing (28 pre-existing failures from v0.8.0)
- No new test failures introduced
- Trailing slash normalization verified in config
- Debug logging outputs verified

Related: IndieLogin.com authentication flow
Following: docs/standards/git-branching-strategy.md

Generated with Claude Code

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

starpunk/__init__.py

@@ -153,5 +153,5 @@ def create_app(config=None):
 
 # Package version (Semantic Versioning 2.0.0)
 # See docs/standards/versioning-strategy.md for details
-__version__ = "0.9.0"
-__version_info__ = (0, 9, 0)
+__version__ = "0.9.1"
+__version_info__ = (0, 9, 1)