Feature: historical anomaly callouts (vs normal)

[Orinks]

Problem

Historical data exists, but users don't get quick context like "warmer/colder than normal" at a glance.

Proposal

Add historical anomaly callouts using existing history support:

• temperature anomaly vs historical baseline
• precipitation anomaly context where available

Why

This adds meaningful context while reusing existing capabilities and avoiding major scope growth.

Scope

• Compare current/near-term values against historical norms
• Add concise anomaly callout in weather summary
• Keep details optional and non-intrusive

Acceptance Criteria

• Temperature anomaly callout shown when sufficient history exists
• Handles missing/partial history gracefully
• No clutter in default view
• Unit tests for anomaly calculations