Fix double slash in Micropub URL construction

- Remove leading slash when constructing URLs with SITE_URL
- SITE_URL already includes trailing slash per IndieAuth spec
- Fixes malformed Location header in Micropub responses
- Fixes malformed URLs in Microformats2 query responses

Changes:
- starpunk/micropub.py line 312: f"{site_url}notes/{note.slug}"
- starpunk/micropub.py line 383: f"{site_url}notes/{note.slug}"
- Added comments explaining SITE_URL trailing slash convention
- Updated version to 1.0.1 in starpunk/__init__.py
- Updated CHANGELOG.md with v1.0.1 release notes

Fixes double slash issue reported after v1.0.0 release.

Per ADR-039 and docs/releases/v1.0.1-hotfix-plan.md

Generated with [Claude Code](https://claude.com/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__ = "1.0.0"
-__version_info__ = (1, 0, 0)
+__version__ = "1.0.1"
+__version_info__ = (1, 0, 1)