chore: restrict LLM model list strictly to 100% Free-Tier Flash models

fix: update active model list to gemini-3.6-flash, 3.5-flash, 3.1-flash-lite, flash-latest

fix: add gemini-2.0-flash model with 1.5-flash fallback and SSE streaming support

fix: update Gemini API model to gemini-1.5-flash and improve error messaging

features- Enhanced Map and what if simlulation and heat pockets.

Fix logo squishing and aspect ratio in AIChat by using scale and flex-shrink-0

Fix horizontal scrolling issue on mobile for the Ask Ritu AI sidebar

Fix weather card cutoff by adding screen bounds detection and scroll

Fix sidebar close button z-index and index.html favicon path

Fix AI Chat expanded modal close button to fully close the sidebar chat

Fix absolute paths for map assets to respect Vite base path

Initial commit of ISRO Climate Twin

Backup before Problem Statement changes