#12666: fix(weather): add precipitation cross-check guidance to prevent misleading rain reports

## Problem The weather skill's Open-Meteo section only shows how to fetch `current_weather`. When agents use `precipitation_probability_max` for rain forecasts, the API can return misleadingly high values (e.g. 65%) even when `precipitation_sum` is 0mm -- meaning no actual rain is expected. This is especially bad during dry seasons. For example, Mexico City in February (deep dry season) returns 65% probability with 0.00mm precipitation sum. An agent naively reporting "65% chance of rain" would be completely wrong. ## Fix Added a "Precipitation: Always Cross-Check" section to the weather SKILL.md: - **Cross-check table**: always compare `precipitation_sum` vs `probability_max` before reporting rain - **Rule**: if `precipitation_sum` is 0mm, ignore the probability entirely - **Example API call** that fetches both fields together - **Seasonal awareness** notes for dry/wet season cities where probability is especially unreliable ## Testing Verified with Open-Meteo API for Mexico City (Feb 9, 2026): - `precipitation_probability_max: 65` - `precipitation_sum: 0.00` - With the new guidance, the agent correctly ignores the phantom probability. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates `skills/weather/SKILL.md` to add explicit guidance for agents using Open‑Meteo daily precipitation fields. It introduces a new “Precipitation: Always Cross‑Check” section that (1) warns against reporting `precipitation_probability_max` in isolation, (2) provides an example Open‑Meteo request that fetches both `precipitation_probability_max` and `precipitation_sum`, and (3) adds a simple interpretation table plus seasonal notes (e.g., dry-season cities) to reduce misleading “chance of rain” reports when forecast precipitation totals are 0 mm. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - Only documentation was changed (weather skill guidance). The added section is self-contained, does not affect runtime behavior, and follows existing doc conventions in the repository. - No files require special attention <!-- greptile_other_comments_section --> _{(4/5) You can add custom instructions or style guidelines for the agent [here](https://app.greptile.com/review/github)!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->