Add `--dry-run` flag to `commit-echo suggest`

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Task summary

Add a --dry-run flag to commit-echo suggest that shows what would be sent to the LLM — the diff, style profile, resolved prompts, and truncation info — without actually making the API call. Useful for debugging custom prompt templates and understanding what data the LLM receives.

Why this is a good first issue

Well-scoped feature that adds a single flag and an early-return path. Teaches CLI option registration with Commander.js, the suggest command flow, and how prompts are assembled. No external API calls needed for testing.

Suggested files or areas

• src/index.ts — Add --dry-run / -n option to the suggest command
• src/commands/suggest.ts — When --dry-run is set, print the diff, resolved prompts, profile summary, and truncation info (if any), then exit without calling generateSuggestions

Acceptance criteria

• commit-echo suggest --dry-run prints the diff, system prompt, user prompt, style profile summary, and truncation info
• commit-echo suggest -n works as an alias
• No API call is made when --dry-run is set
• Without --dry-run, behavior is unchanged
• npm run build passes with no errors

Extra context

• Follow the existing flag pattern in src/index.ts (e.g., --verbose, --commit, --yes)
• The showVerboseInfo() and showTruncationWarning() functions in src/commands/suggest.ts demonstrate how to print diagnostic info using pc.dim() / pc.yellow()
• resolveSystemPrompt() and resolveUserPrompt() in src/llm/prompt.ts can be called directly to show the resolved prompts
• Use pc.dim() for the diff and prompt output to distinguish it from normal output

[nightcityblade]

Hi, I'd like to work on this. I'll submit a PR shortly.