Set up the release/1.x support branch before 2.0 #119

Plan: P6-3 · Phase 6 · Priority P3 · Decisions: D13

Scope

The support-branch setup when 2.0 approaches. When 2.0.0 is released, 1.x gets security fixes for 6 months from release/1.x, made from the last v1.* tag (D13; docs/RELEASE-PROCESS.md, added in #102). Before that release:

• ADR-0008: a superseding ADR through /adr (from 1.0 on). Today it makes main the only public ref and defines release/… as a branch from develop into main; a long-lived, published release/1.x changes both.
• Versioning: ^refs/heads/release/1\.x$ in publicReleaseRefSpec (version.json), so builds of that branch get stable 1.x.y versions.
• Publishing: a release/1.x trigger in nuget-release.yml, and the publishing environment's branch rule allowing it.
• CI and protection: build.yml, format.yml, dependency-review.yml and release-label.yml run on PRs into release/1.x; the ruleset protects it like main (required checks, PR only); the release-notes check in build (net10.0) also covers PRs into release/1.x.
• Process: RELEASE-PROCESS describes a 1.x security fix (hotfix/… from release/1.x → PR into release/1.x → release); /prepare-release and the hotfix steps say which line they target.

Found by the reviewer of #102 (PR #173).

Done when

• The PR (body starts with Closes #<this issue>) is merged into develop.
• dotnet build OpenUrzednik.slnx, dotnet test OpenUrzednik.slnx -f net10.0 and dotnet format OpenUrzednik.slnx --verify-no-changes pass (format only after a clean build); on Windows also -f net472 for build, TFM and API changes.
• The reviewer agent reports no blocking issue; ADR decision changes went through /adr; every CLAUDE.md, reviewer or skill rule this change contradicts is updated in the same PR.
• Docs: English is the base; README.pl.md changes only where an informational part is affected (/stop-slop on English, /miodkuj on Polish).

Who

An agent prepares the PR; the maintainer reviews and merges it. Agents follow CLAUDE.md and the project's rules (start only when Status is Ready, set In progress, never close this issue yourself).