Extend basectl test with dry-run, mise task, and current project support

[codeforester]

Goal

Carry forward the useful follow-up ideas explored in the closed duplicate PR #235 without replacing the simpler implementation that shipped in #233.

Scope

• Add basectl test --dry-run so users can inspect the resolved project test command without running it.
• Allow manifests to declare a mise-backed test task, for example:

test:
  mise: test

Base should delegate this to mise run test from the project root.

• Allow basectl test with no explicit project when the current directory is inside a Base-managed project, using the nearest base_manifest.yaml.

Non-goals

• Do not introduce a separate base_test Python package unless the Bash-centered implementation becomes hard to maintain.
• Do not add conventional test runner guessing yet.
• Do not change the already-working test.command behavior from Add basectl test command #233.

Context

PR #235 was closed unmerged because #233 had already implemented #119. This issue preserves the useful extra ideas from #235 as an incremental follow-up.