feat: add shell tab completion for bash, zsh, and fish

[Copilot]

No tab completion existed for the halo CLI. This adds a halo completion command that emits shell hook scripts and handles the inline completion callback shells invoke on every Tab press.

New: halo completion command

• halo completion bash|zsh|fish — prints a shell-specific completion hook script to stdout; users source it in their rc file or drop it into the fish completions directory
• halo completion -- <words…> — the internal callback invoked by the hook on every Tab; returns newline-separated candidates to stdout

Completion logic (src/commands/completion/index.ts)

• Static TOP_LEVEL_COMMANDS + SUBCOMMANDS maps covering all 12 command areas and their full subcommand trees, including two-level namespaces (auth profile, comment reply)
• computeCompletions(words) handles both invocation modes:
  • bash/zsh: reads COMP_LINE + COMP_POINT env vars for cursor-aware tokenization
  • fish: uses the explicit word array passed by the hook
• Partial-word prefix filtering; bails cleanly when context contains option flags or exceeds supported nesting depth

Setup

# Bash — add to ~/.bashrc
eval "$(halo completion bash)"

# Zsh — add to ~/.zshrc
eval "$(halo completion zsh)"

# Fish
halo completion fish > ~/.config/fish/completions/halo.fish

After sourcing, halo po<TAB> → post; halo post <TAB> → list get create update delete open import-json export-json.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>期望支持按 tab 进行命令联想</issue_title>
<issue_description>类似于 npm 一样，输入 npm in 时按下 tab，会对所有可用的命令进行联想然后列出，方便使用。

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes 期望支持按 tab 进行命令联想 #3

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