Add --show-diff flag to commit-echo suggest

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Problem

When running \commit-echo suggest, the diff is silently sent to the LLM. Users have no visibility into what diff is being analyzed — whether it was truncated, which files are included, or the actual content being sent.

Proposed Solution

Add a --show-diff\ flag (or -d) to the \suggest\ command that prints the raw diff before generating suggestions. This complements the existing --verbose\ flag (which shows model, style profile, and truncation stats) by showing the actual diff content.

Implementation Notes

• Add the flag to the \suggest\ command options in \src/index.ts\
• In \src/commands/suggest.ts, print the diff content using \pc.dim()\ before calling \generateSuggestions\
• Include truncation information if the diff was truncated

Acceptance Criteria

• --show-diff\ flag is accepted by \commit-echo suggest\
• The raw diff is printed before generating suggestions
• If diff was truncated, the truncation marker is visible in the output
• Works with both staged and unstaged diffs