docs: update TEST_COVERAGE_PLAN with accurate completion status

Corrected the description of getRemoteUrl tests to reflect that:
- No default fallback was added (unnecessary - defaults are merged in prepareOptions)
- Tests verify the function works when remote is provided from defaults
- Clarified that prepareOptions() already merges defaults.remote='origin'

This makes the plan accurately reflect the implementation rather than
describing a removed fallback that was deemed unnecessary.

Author: JohannesHoppe

TEST_COVERAGE_PLAN.md

@@ -173,10 +173,10 @@ Add `"types": "index.d.ts"` to package.json
 - ✅ Test: getRemoteUrl() returns correct URL from git config
 - ✅ Test: Error when not in a git repository
 - ✅ Test: Error when remote doesn't exist
-- ✅ Test: Works with minimal options (defaults to 'origin')
+- ✅ Test: Works when remote is provided from defaults
 - ✅ Test: Returns consistent URL for same remote
 - ✅ Test: Passes remote option to gh-pages getRemoteUrl method
-- ✅ Fixed: Added default 'origin' remote when undefined to prevent undefined string conversion
+- ✅ Note: No default fallback needed - prepareOptions() merges defaults.remote='origin'
 
 **Why Critical:** This internal API could break in gh-pages v6+ upgrade