Keep Bash and Zsh completions in parity with nested command help

[codeforester]

Problem

Shell completions are hand-maintained and have drifted from live nested help. Current tests cover top-level parity and selected Bash examples, but they do not catch nested Zsh drift or newer option gaps.

Evidence

• Zsh workspace completion still lists only status check doctor clone pull, missing init and configure.
• Zsh repo completion omits clone from the repo command list.
• Bash completion misses newer options such as --copy-project-fields-from, repo init --pr, check --manifest, check --remote-network, and doctor --no-color.
• Existing Bash completion tests assert some stale option sets, so the drift is not caught.

Desired outcome

Bash and Zsh completions should match the public command/help surface for nested commands and options.

Scope

• Update Bash completions for missing nested options.
• Update Zsh completions for missing nested commands and options.
• Add tests that compare nested completion surfaces against command help or a shared command spec.
• Update contributor docs if a manual completion update checklist remains necessary.

Acceptance criteria

• Zsh completes workspace init, workspace configure, and repo clone.
• Bash completes all options shown by command-specific help for check, doctor, repo init, and repo configure.
• Tests fail when a nested command is added to help without corresponding completion coverage.
• Completion behavior continues to complete project names where supported.