Harden argument validation in knife bootstrap with structured error messages

[nikhil2611]

Epic

Part of Crawl Track backlog epic.

Background

Ex5 (API Hardening) improved validation in several commands. knife bootstrap is the highest-risk command (executes remote code) and still has gaps: invalid node names, missing required flags, and conflicting options produce cryptic errors or silent failures.

Code Paths

• lib/chef/knife/bootstrap.rb — #validate_options! and #run
• lib/chef/knife/bootstrap/train_connector.rb — connection validation
• spec/unit/knife/bootstrap_spec.rb — existing tests (expand these)

Acceptance Criteria

• validate_options! raises Chef::Exceptions::InvalidBootstrapArguments (or equivalent) with a human-readable message for: missing host, invalid node name chars, conflicting --sudo + --no-sudo
• Error messages include the offending value and a hint (e.g. "Node name bad name contains spaces — use hyphens instead")
• New specs cover each validation branch
• No change to happy-path behavior

Dependencies

• Depends on: Ex5 API hardening patterns (already merged)
• Blocks: nothing

Estimated Size

Medium