docs(changelog): format the 1.0.0 entry (#6)

Release PR #4 was merged before the release workflow learned to format
release-please's changelog headers (#5), so master's 1.0.0 entry kept
release-please's format and CI's changelog check fails on master. This
applies the same rewrite the release workflow now does on release PRs.

Changes:
- CHANGELOG.md: `## [1.0.0](compare-url) (2026-10-09)` → `## [1.0.0] -
09.10.2026.`, `### ⚠ BREAKING CHANGES` → `### BREAKING CHANGES`

Tests: the CI release-guard check passes locally against
.release-please-manifest.json (1.0.0).

Author: kvs-coder

CHANGELOG.md

@@ -1,9 +1,9 @@
 # Changelog
 
-## [1.0.0](https://github.com/kvs-coder/SamsungHealthReporter/compare/0.0.6...1.0.0) (2026-10-09)
+## [1.0.0] - 09.10.2026.
 
 
-### ⚠ BREAKING CHANGES
+### BREAKING CHANGES
 
 * rebuild SamsungHealthReporter on the Samsung Health Data SDK ([#3](https://github.com/kvs-coder/SamsungHealthReporter/issues/3))