feat: add real-time weather monitoring agent (Closes #131)

[AKIB2005]

Summary

Adds a beginner-friendly Real-time Weather Monitoring Agent under contributors/weather-monitor-agent/. The agent accepts a city name via the uAgents chat protocol, fetches live weather data from OpenWeatherMap free tier (no credit card required), and returns temperature, humidity, wind speed, and condition. Fires a configurable heat alert when temperature crosses a threshold.

Type of Change

• New agent example
• Bug fix
• Documentation update
• Refactor / cleanup
• Other

Checklist

• I have starred this repository.
• New community agents are under contributors/<agent-name>/ (not repo root).
• I ran ruff check ..
• I ran ruff format ..
• I added/updated README.md for changed example(s).
• I added .env.example if environment variables are required.
• I added demo image/GIF (if applicable).
• I added agent profile link (if applicable).
• I updated contributors/CHANGELOG.md for community agent changes, or root CHANGELOG.md for other non-doc changes.
• I added my agent to the Community Contributors table in root README.md (if new agent).
• I verified paths/commands used in docs.
• I understand this PR requires maintainer review before merge (review-required CI).

Related Issue

Closes #131

Notes for Reviewers

• Uses OpenWeatherMap free tier API (no credit card, instant signup)
• Fully commented code, designed for first-time uAgents contributors
• Configurable temperature alert threshold via .env
• Works locally without Agentverse key; registers on Agentverse when key is provided
• ruff check and ruff format to be run before final merge if required