[Feature Request] Scoped style/instruction customization for AI suggestion prompts

Description TL;DR The built-in AI suggestion prompts (title, tags, correspondent, etc.) are fixed in code, with no way to adjust their output style. A prior request for a fully free-editable prompt override (#12871) was closed as not planned — likely because replacing the whole prompt risks breaking the structured JSON contract the suggestion feature relies on. This proposal is narrower: small, additive "style/instruction" settings per suggestion type, injected into the existing Jinja2 prompt templates alongside the schema-enforcing instructions, which stay untouched. Is your feature request related to a problem? Please describe. Users who use the built-in AI suggestions with different LLMs or organizational conventions (e.g. short vs. descriptive titles, specific tag casing, domain-specific terminology) have no way to adjust the *style* of the output. This is distinct from #12871, which asked for a full prompt override — that request was cl…