chore(release): add 0.7.12 changelog entry

Folds all changes since 0.7.10 into 0.7.12 (0.7.11 was unpublished from
npm): size-adaptive codegraph_explore output budget (#185/#187), line
numbers in explore source sections (#188), explore-first tool guidance
(#191), language-neutral source-omission markers, and Kotlin/Swift
test-file detection (#191).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -7,7 +7,7 @@ a [GitHub Release](https://github.com/colbymchenry/codegraph/releases) tagged
 This project follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/)
 and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [0.7.12] - 2026-05-20
 
 ### Added
 - **MCP / explore**: `codegraph_explore` source sections now carry line
@@ -72,6 +72,8 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   `Call.kt`, `OkHttpClient.kt`, `Request.kt`, `Response.kt`). Capital-led
   matching keeps production files like `latest.kt` / `manifest.kt` unflagged.
 
+[0.7.12]: https://github.com/colbymchenry/codegraph/releases/tag/v0.7.12
+
 ## [0.7.10] - 2026-05-19
 
 ### Fixed