feat(changelog): one source file per release, generated outputs

Release notes now live in changelog/<version>.md (front matter with
version and date, then ## App and ## VS Code sections grouped into
New, Improvements, Fixes, Misc) plus changelog/unreleased.md for what
has not shipped. `bun run changelog:build` renders CHANGELOG.md,
packages/vscode/CHANGELOG.md, and changelog/index.json from them;
`changelog:check` fails when the outputs are behind and runs in CI and
in release:prepare. `oc-dev create-release` promotes unreleased.md to
the versioned file dated today and rebuilds.

The existing history was split mechanically: every bullet kept, sorted
into groups by keyword, five hand-typed headers with one-digit days
normalised to YYYY-MM-DD (the update dialog matched none of them). The
generated files keep today's release headers, which the update dialog,
the release workflow, and the website match by regex.

Claude-Session: https://claude.ai/code/session_01VqV56Hez25hTxXH4ipJfzH

changelog/1.8.7.md

@@ -0,0 +1,19 @@
+---
+version: 1.8.7
+date: 2026-03-13
+---
+
+## App
+
+### Improvements
+- CLI: hardened entrypoint detection across direct, symlinked, and shim-based launches to keep startup behavior consistent across package managers (thanks to @shekohex).
+- Deployment/Docker: improved `docker run` startup behavior and entrypoint handling (thanks to @nzlov).
+
+### Fixes
+- CLI: fixed a startup regression in global npm/bun installs where wrapper or symlinked `openchamber` entrypoints could exit without output on commands like `--version` or `status`.
+- Windows/Web: daemon startup and Git operations no longer flash extra console windows (thanks to @SergioChan).
+
+## VS Code
+
+### Improvements
+- No notable changes.