Show custom prompt template status in `config` output

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Task summary

After commit-echo init, the wizard summary shows whether custom systemPromptTemplate / userPromptTemplate are set. The config command does not display this status, even though those keys are configurable via config set.

Why this is a good first issue

Small UX improvement — largely copy-paste from init.ts into config.ts. One file change with a visible result when running the CLI.

Suggested files or areas

• src/commands/config.ts
• src/commands/init.ts — reference for how templates are displayed
• tests/config-command.test.mjs — extend with assertion

Acceptance criteria

• commit-echo config shows whether custom prompt templates are set (e.g. "custom" vs "default")
• Output is clear and consistent with init wizard summary
• Existing config tests still pass; add test coverage if practical

Extra context

config --json already includes systemPromptTemplate and userPromptTemplate keys in the raw output — this issue is about human-readable config display.