Build a single-page aquarium stocking tool that helps hobbyists figure out how many fish can safely live in their tank.

**The scenario:** A new fish keeper has a tank and wants to know if their planned fish collection will overcrowd it. They need a quick, friendly calculator to check compatibility.

**What to build:**
- An input for tank size in gallons (number field)
- A small list of common fish presets (e.g. Goldfish = 10 gal each, Guppy = 1 gal, Betta = 5 gal, Neon Tetra = 2 gal, Angelfish = 10 gal) displayed as clickable cards or a dropdown
- The user adds fish one at a time (pick a species, set a quantity, click Add)
- A running list shows the fish added so far with a remove button per row
- A live capacity bar or gauge shows total gallons used vs. available, turning green when safe, yellow when near the limit (>80%), and red when overstocked
- A simple text summary like "Your 20-gallon tank can fit 3 more Neon Tetras" or "⚠️ Overstocked by 5 gallons!"

No backend, no auth, no persistence needed — everything lives in the page's state.