Adopt Base-specific debugging and verification guidance

[codeforester]

Problem

Base fixes around basectl setup, check, doctor, build, test, workspace discovery, and runtime shell behavior benefit from a more explicit root-cause and verification discipline. The obra/superpowers systematic-debugging and verification-before-completion skills are a useful reference, but Base should adopt only the parts that fit its existing workflow.

Reference:

• https://github.com/obra/superpowers/blob/main/skills/systematic-debugging/SKILL.md
• https://github.com/obra/superpowers/blob/main/skills/verification-before-completion/SKILL.md

Desired Outcome

Document a Base-specific debugging and completion-verification workflow that requires fresh evidence before claiming a fix is complete.

Scope

• Add Base-specific guidance for reproducing failures, reading full error output, tracing root cause, and testing one hypothesis at a time.
• Add guidance for component-boundary diagnostics when failures cross shell, Python, manifest, runtime, or project-command layers.
• Add a completion gate that says which command output is required before claiming success.
• Prefer examples from Base command families such as basectl doctor, basectl setup, and basectl test.

Non-Goals

• Do not install or vendor the Superpowers plugin.
• Do not require the full Superpowers methodology for every Base change.
• Do not change basectl doctor behavior as part of this documentation issue unless the implementation work naturally becomes a separate follow-up issue.

Acceptance Criteria

• Base documentation or skills.md includes a Base-specific debugging and verification workflow.
• The workflow explains how to move from symptom to root cause before fixing.
• The workflow explains what fresh verification evidence must appear in PRs and final summaries.
• The guidance keeps basectl check and basectl doctor non-mutating.

Validation

• Run git diff --check.
• If only documentation changes are made, no code test suite is required.

Demo Impact

None. Documentation/process adoption only.