Establish the copick-mcp test, transport, and packaging gate #53

Parent epic: #52

Objective

Establish a deterministic MCP, transport, and packaging gate on the current stable copick 1.x / copick-utils 1.x stack before changing runtime floors or CLI integration.

The repository currently declares a test extra but has no tests/ directory, no test workflow, and no committed lockfile.

Work

• Add deterministic local project fixtures and a committed uv.lock.
• Cover all 14 public MCP tools, including success, empty, and structured-error paths.
• Cover the three copick.setup.commands entry points using only temporary desktop/code-global/code-project configuration paths.
• Cover core commands, nested core subcommands, utility plugin commands, command details, and valid/invalid syntax parsing.
• Add an in-process FastMCP client test that lists all tool names and exercises schema/result serialization.
• Assert import, tool calls, Click parsing, and MCP startup place no non-protocol content on stdout.
• Preserve the current metadata exploration result against the available legacy local fixture.
• Record the missing setup/download groups and --help stdout/exit behavior as migration cases for the next issue rather than desired compatibility behavior.
• Add an unconditional pull-request matrix on final CPython 3.11, 3.12, 3.13, and 3.14.
• Make the workflow reusable with an exact commit SHA for release validation.
• Build a baseline wheel/source distribution and verify all three setup entry points are present.

Tests should exercise behavior. Do not add AST/source-grep tests or tests that parse dependency declaration strings.

Acceptance criteria

• The current stable-resolution behavior suite passes from a clean locked install.
• All 14 MCP tools and three setup entry points have executing coverage.
• In-process FastMCP schemas/results are serializable.
• The suite detects direct stdout leakage.
• Every pull request, including documentation-only changes, receives the stable-Python matrix.
• The workflow can validate an exact release SHA.
• Baseline distributions build and contain the registered setup entry points.

Non-goals

• No dependency-floor migration in this issue.
• No direct Zarr compatibility code.
• No fix for the known CLI group/help defects until the next stack layer.