feat: print one project's version with version --current --project-name

[philasmar]

version --current can only produce a capturable value for a single-project repository. With several projects it prints them labeled:

Project1: 1.2.3
Project2: 4.5.6

which is readable but not assignable, so VERSION=$(autover version --current) silently becomes multi-line text. A pipeline publishing more than one artifact from one repository has no way to ask for the version it needs.

This adds --project-name to version, meaningful alongside --current:

VERSION=$(autover version --current --project-name "Project2")   # 4.5.6

Bare output regardless of how many projects are configured. The name matches exactly as change --project-name already does.

Why it came up

A container-image repository that builds two images from two Dockerfiles. Two projects with their own Path gives them independent versions, which is what you want — but then the publish step can't read either one. The alternatives were worse: parse the labeled display format in shell, or collapse both images onto one version they don't actually share.

Behaviour

• Unknown name is an error, listing the configured names, rather than empty output. Left unvalidated, a typo sets VERSION="" and publishes an untagged or mis-tagged artifact — a silent failure in exactly the place it hurts.
• Paths drift is an error. A project using Paths shares one version across its files by definition. If those files disagree, printing the first would quietly publish a version that doesn't match what's in the other file, so it says so instead.
• VersionFromTag already prints a single repository-wide version; naming a project there is redundant but still validated, so a typo is caught rather than ignored.
• Omitted, nothing changes.

Tests

Three added to VersionCommandTests, alongside the existing single-project --current test:

• M — several projects without --project-name still print labeled. Asserts the contract the new option exists to work around, which had no coverage at all.
• N — --project-name prints that project bare, with nothing about the other one.
• O — unknown name exits UserError, names what is configured, no stack trace, empty stdout.

Full suite: 103 integration, 190 unit, 0 failures.

Note for anyone running these locally: dotnet test reports "Zero tests ran" for these projects — TUnit builds self-hosting test executables, so run test/AutoVer.IntegrationTests/bin/Debug/net10.0/AutoVer.IntegrationTests directly (optionally with --treenode-filter).