Feature: weather impact summaries (outdoor/driving/allergy) #324
Description
Problem
AccessiWeather provides great raw weather details, but users still need quick "what does this mean for me" guidance.
Proposal
Add weather impact summaries derived from existing data:
- outdoor comfort/activity guidance
- driving caution flags (visibility/freezing/wind/precip)
- allergy caution (pollen + wind context)
Why
High-value user-facing insight without adding new providers or heavy UI.
Scope
- Rule-based impact scoring from existing forecast/environmental fields
- Short plain-language summary in current/forecast sections
- Keep explanations transparent (no opaque AI-only decisions)
Acceptance Criteria
- Impact summary appears in current and forecast views
- Rule set documented and unit-tested
- No additional API dependencies required
- Screen-reader output remains concise and clear