ci(release): add stable release pipeline

[crup]

Implements the final stable release pipeline preparation branch.

Changes:

• Adds a multi-stage stable release workflow with visible guard, verify, publish, and GitHub release jobs.
• Keeps stable publishing manually locked to main with confirm_stable_release=publish-stable.
• Adds a stable_version input, defaulting to 0.0.1 for the first stable version.
• Blocks duplicate npm publishes before running pnpm publish --tag latest.
• Adds package SEO metadata: homepage, repository, bugs URL, and expanded npm keywords.
• Documents the release flow in the README and release channels docs.

Recommendation:

• First stable should be 0.0.1, not 1.0.0, because the project already has the 0.0.1-alpha.x prerelease line and should keep the stable release semver-continuous.

Validation run locally:

• pnpm typecheck
• pnpm test
• pnpm build
• pnpm docs:build
• pnpm readme:check
• pnpm size
• pnpm pack --dry-run
• git diff --check

[github-actions]

Bundle size report

Entry	Files	Raw	Gzip	Brotli	Raw delta	Gzip delta	Brotli delta
core	2	4.44 kB	1.52 kB	1.40 kB	0 B	0 B	0 B
timer group add-on	3	10.93 kB	3.83 kB	3.50 kB	0 B	0 B	0 B
schedules add-on	3	8.62 kB	3.02 kB	2.78 kB	0 B	0 B	0 B
duration helper	1	318 B	224 B	192 B	0 B	0 B	0 B
diagnostics helper	1	105 B	115 B	90 B	0 B	0 B	0 B
core CJS	1	4.71 kB	1.63 kB	1.50 kB	0 B	0 B	0 B
timer group CJS	1	11.02 kB	3.86 kB	3.54 kB	0 B	0 B	0 B
schedules CJS	1	8.71 kB	3.04 kB	2.81 kB	0 B	0 B	0 B
duration CJS	1	808 B	475 B	424 B	0 B	0 B	0 B
diagnostics CJS	1	605 B	367 B	326 B	0 B	0 B	0 B