fix(completions): install bash completions into all login + non-login rc files

[sachiniyer]

Summary

• rc_path for bash picked a single rc file (preferring .bashrc), but bash login shells read .bash_profile / .bash_login instead — so on macOS Terminal and SSH setups where both files exist, completions never loaded in login shells.
• Mirror rustup: append the snippet to every existing bash rc file (.bash_profile, .bash_login, .bashrc), creating .bashrc if none exist. Each file is checked independently for the snippet and skipped if already present, so re-runs and partial installs converge.
• Factored installation into a small install_snippet helper and bash_rc_paths helper so the per-file idempotency and the bash file-selection logic are unit-testable.

Fixes #267.

Test plan

• cargo fmt --check
• cargo clippy -- -D warnings (matches CI)
• cargo test --lib — 298 passed, including new cases:
  • bash_rc_paths_only_bashrc
  • bash_rc_paths_only_bash_profile
  • bash_rc_paths_both_exist
  • bash_rc_paths_all_three_exist
  • bash_rc_paths_neither_exists_creates_bashrc
  • install_snippet_appends_to_new_file
  • install_snippet_preserves_existing_content
  • install_snippet_is_idempotent
  • install_snippet_per_file_idempotency_across_bash_rcs

🤖 Generated with Claude Code

[cubic-dev-ai]

No issues found across 1 file

[sachiniyer]

Closing — taking a different approach. Rather than a multi-file dotfile installer (rustup-style), we're going to switch detail completions to the print-and-source pattern that kubectl, gh, terraform, etc. use: emit the completion script to stdout, document source <(detail completions bash). That sidesteps the rc-file-discovery question entirely and matches user expectations from other CLIs. Will open a follow-up PR addressing #267 with that approach.