docs: consolidate one running changelog

[tolibear]

What changed

• made CHANGELOG.md the single canonical running release history
• consolidated the complete GoalBuddy package line and earlier Goal Maker history into that file
• corrected headings and dates against live npm and GitHub release state
• retained the major 0.3.0, 0.3.5, 0.3.7, and 0.4.0 release artwork
• noted where 0.4.3 superseded Claude Code's old GoalBuddy /goal behavior
• removed eight duplicate per-version release-note files
• updated README, contributor guidance, and the release process to point to the running changelog
• added a regression test that rejects future per-version changelog files and requires all published version sections and release images

Why

Release history had split across CHANGELOG.md, eight files under docs/releases/, GitHub Releases, and npm publication dates. That allowed title, date, publication-state, and command behavior to drift. One running changelog gives contributors one durable place to update and readers one complete history.

Verification

• Node 24.19: npm run check (133 tests passed)
• Node 24.19: npm run pack:dry-run
• git diff --check
• live npm verified goalbuddy@0.4.3 is latest
• live GitHub verified v0.4.3 was published on 2026-08-05

This is documentation and test-policy only. Package and plugin versions remain 0.4.3.