chore: remove CHANGELOG.md in favor of generated release notes

[thymikee]

Summary

Remove CHANGELOG.md. Release notes come from GitHub's generated notes, built from PR titles. Nothing reads the file.

The file stopped working as a changelog. Everything from 0.15.0 to 0.21.13 sat under one Unreleased heading, so it could not tell a reader which release shipped a change. Every PR also added an entry at the same line, which caused rebase conflicts and bad merges: #2901's rebase conflicted only there, and #2865's rebase pasted stale lines back in.

Also:

• The 6 workflows drop CHANGELOG.md from paths-ignore, and the root-docs pin test drops it from its list.
• The gesture deprecation policy now says "release notes" instead of the file.
• ADR mentions stay as they are, because they record history.

Put user-impact prose in the PR body. Open PRs that add a CHANGELOG entry drop that hunk on rebase.

9 files touched.

Validation

At 5016c73: pnpm check:affected --run passed. After the rebase onto main (1bd8dc8; the only conflict was the deleted CHANGELOG), the full gate hit contention failures on a heavily loaded host (load average above 500). The two checks it reported, check:tmpdir-leaks:test and the scripts/gate tests, both passed when run alone. Docs and CI config only, so no device run applies.

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-09-24 16:37 UTC

[github-actions]

Size Report

Metric	Base	Current	Diff
Installed (including dependencies)	4.81 MB	4.81 MB	0 B
Package (unpacked)	4.80 MB	4.80 MB	0 B
Package (download)	1.44 MB	1.44 MB	+16 B

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	21.7 ms	21.7 ms	+0.0 ms
CLI --help	61.5 ms	61.3 ms	-0.2 ms