[FEAT cloudctl] - Add foreach command with context selector and parallel execution #73

User Story

As a cloudctl user, I want to run a kubectl command across many clusters at once, so I can perform fleet-wide operations and compliance checks efficiently.

Description

cloudctl foreach --selector <sel> kubectl <args> — filters kubeconfig contexts using label-style selectors, shows a confirmation prompt, then runs the command in parallel across all selected contexts with per-context prefixed output and fail count aggregation.

Selector syntax: name=VALUE, name!=VALUE, name in (a,b,c), name notin (a,b,c), name~=REGEX, name!~=REGEX. Empty selector matches all contexts.

Acceptance Criteria

• Context list read from kubeconfig
• All selector syntaxes supported
• Confirmation prompt shown unless --quiet / -q
• Commands run in parallel across selected contexts
• stdout/stderr output prefixed with [context-name]
• Exit with error if any execution fails; total failure count reported

Reference Issues

Epic: #70