Extract groomer LLM prompts to dedicated files

[itsmiso-ai]

Parent umbrella issue: #616
Source audit: Weekly tech debt audit: dispatch - 2026-07-15
Source audit date: 2026-07-15

Recommendation

Problem: The groomer's LLM system prompt is embedded as a 188-line string in src/lib/groomer/llm.ts, making prompt versioning, diff review, and A/B testing harder than necessary.

Evidence:

• src/lib/groomer/llm.ts lines 18–205: const SYSTEM_PROMPT = ... template literal

Acceptance: Move the prompt content to a dedicated file under src/lib/groomer/prompts/ and reference it from llm.ts. Prompt content should be reviewable as a diff when changed.