docs: write the 3.0.0 release notes, and let Release take an explicit bump

[BernardJen]

Groundwork for the 3.0.0 release. Two blockers.

The changelog stopped at 2.13.0

Everything from 2.14.0 to 2.19.0 shipped without being written up, and the stale [Unreleased] block still described that work as pending. It also carried two claims that are no longer true:

• the screensaver set is 29, not 30
• Mandelbrot no longer exists as its own saver — Julia Family absorbed it in feat: combine the Julia and Mandelbrot screensavers into one paired view #209, but the entry still described a standalone Mandelbrot rewrite

Both corrected. The 3.0.0 entry leads with the wall performance work, since that is the substance of the release, and records what was ruled out — software rendering, the detection downscale, resize() layout, the capture service — so nobody spends another evening re-investigating them.

Release could not express a major

The bump is derived from commit subjects (%s, so a BREAKING CHANGE: body footer is never even seen), and force_release only rescues a none bump — it cannot raise the level. The only way to ship 3.0.0 with the workflow as it stood was to write !: into a commit subject.

That would claim a breaking change, and there isn't one. I checked: no settings key or launch flag was removed, and nothing persists a screensaver name, so Julia Family replacing two registry entries is invisible to an existing settings.json. 3.0.0 is a milestone, not a break — the notes say so plainly.

So Release now takes an explicit bump input (auto/patch/minor/major). It skips analysis rather than overriding it afterwards, so a run with no qualifying commits still honours the request instead of taking the none early exit. This also fixes the longer-standing gap where a deliberate patch or hotfix had no way to be expressed.

Verification

• 699 tests green, lint clean.
• release.yml parses, and both dispatch inputs resolve (force_release, bump).
• Changelog heading structure checked: v3.x → 3.0.0, v2.x → 2.13.0 and older, legacy v1.x intact.

Merging this only lands the notes and the input. The release itself is a separate workflow_dispatch with bump: major — and the input has to be on main before it can be selected.

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