Prepare remove-markdown 0.7.0 stable release

[zuchka]

Summary

• promote the soaked 0.7.0-rc.1 package metadata to stable 0.7.0
• date the 0.7.0 changelog entry for August 31, 2026
• add comprehensive, post-ready release notes at .github/release-notes/0.7.0.md

Soak review

• 0.7.0-rc.1 has been published under next since August 26
• no GitHub issues or compatibility PRs were opened during the soak window
• npm latest remained on 0.6.4
• the RC.1 browser-native ESM fix remained publicly installable and verified

Stable release validation

• confirmed 0.7.0 is available on npm
• synchronized package.json and root lockfile metadata
• complete prepublishOnly gate
• existing 39-test behavior suite
• CommonJS, ESM, packed-tarball, and TypeScript tests
• Are the Types Wrong validation
• differential comparison with published 0.6.4
• esbuild and Rollup browser-targeted bundles
• Deno source, HTTP URL-module, and packed npm-package tests
• zero production audit findings
• successful npm publish --dry-run --tag latest --access public
• expected eight-file npm tarball; release notes remain repository-only

Release notes

The included notes provide:

• user-facing highlights and migration expectations
• CommonJS, Node ESM, browser ESM, and Deno examples
• the RC.0 to RC.1 hardening story
• compatibility and validation evidence
• project scope and contributor credit
• concise post-ready announcement copy

After merge

Publish a non-prerelease GitHub Release tagged 0.7.0 from the merged commit, using .github/release-notes/0.7.0.md. The release event will trigger the trusted publishing workflow and move npm's latest tag to 0.7.0.

This PR does not publish the package by itself. Performance issue #118 remains separate.