release: 3.0.0

[raspbeguy]

Promotes v3.0.0-rc3 to the first stable v3. VERSION to 3.0.0, a [3.0.0] changelog section on the 2.0.0 model with the three RC entries kept below it, and the regenerated spec.

No code or spec change since rc3. src/, cli/, files/, the generator and build/openapi.json are byte-identical to the tag that was installed from its published APK and verified on a device, so what ships is what was soaked.

What the section claims, and why each number is checked

Both figures in it are the sort that rot, and I wrote a stale one on the first pass: the summary said 49 curated resource endpoints, which is 2.5.1's count. 3.0.0 removed vnstat/interfaces, so it is 48. Corrected and verified against the generated spec, alongside the test count:

spec says 48 curated endpoints, changelog says 48   match
suite reports 1230 unit tests, changelog says 1230  match

Readiness

• Provider live-tested against rc3 with nothing filed.
• The migration guide's section that promised silence where v3 returns 422 is corrected and merged.
• Rollback is documented truthfully: the feed carries the current release only, and the site's install page now offers per-version instructions, so 2.5.1 keeps working steps as it leaves the feed.
• The README quickstart a reader pastes now works, and all 16 shipped examples run green against a device.
• lint, 1230 unit tests, openapi-check, coverage and gate-selftest (11 gates, each mutation-probed) pass on this commit.
• Nothing in the tree still calls itself an RC.

After this merges

The signed tag is created separately, per the release process. Promotion also has two effects worth watching, both verified afterwards rather than assumed: the feed switches from 2.5.1 to 3.0.0, so a routine apk upgrade uapi moves an operator's mount to /api/v3, and the org site regenerates its own facts from the new stable release, flipping every /api/v2 reference without an edit.