Complete alpha validation and release napari-copick 2.0

[uermel]

Parent Epic: #39
Implementation PR: #45

Goal

Complete the source behavior gate, publish napari-copick alphas from v2.0, and later finish stable 2.0 after final runtime prerequisites exist.

Scope

• Use the existing v2.0 alpha Release Please configuration.
• Merge the behavior migration after its cross-platform source CI passes.
• Bootstrap 2.0.0-alpha.1 deliberately with Release-As.
• Build and publish from the exact Release Please SHA through the normal release workflow.
• Keep README documentation accurate for OME-Zarr 0.4/v2 reads, OME-Zarr 0.5/v3 delegated writes, and eager selected-level loading.
• Before stable 2.0.0, synchronize v2.0 with main, require final copick and shared-UI 2.x runtime floors, and rerun the source behavior matrix.

Test-scope decision

Do not add tests that install published napari-copick artifacts, wheel/sdist metadata inspection, dependency-bound assertions, AST/source guards, or sibling-package coexistence jobs.

Acceptance criteria

• Pull-request source behavior CI passes on the declared Python/OS matrix.
• Release automation creates alphas only from v2.0 and stable releases only from main.
• Documentation matches actual eager, metadata-driven behavior.
• Stable napari-copick 2.0.0 is not published before final copick and shared-UI 2.0 runtime artifacts pass the same source behavior matrix.

Alpha publication remains blocked on merging the implementation and completing its source CI.

[uermel]

Source-gate update (2026-08-18): PR #45 is mergeable and its complete Python 3.11-3.14 behavior matrix is green. Alpha publication was intentionally not triggered from the implementation PR; after merge, this issue tracks the deliberate Release-As bootstrap for 2.0.0-alpha.1.