Phase 1: Chemistry engine — elements, compounds, reactions

- 20 real elements from periodic table (H through Hg) with accurate data
- 25 compounds with game effects (NaCl, H₂O, gunpowder, thermite, etc.)
- 34 reactions: synthesis, combustion, acid-base, redox, decomposition
- Reaction engine with O(1) lookup by sorted reactant key
- Educational failure reasons (noble gas, missing heat/catalyst, wrong proportions)
- Condition system: temperature, catalyst, energy requirements
- 35 unit tests passing, TypeScript strict, zero errors

Co-authored-by: Cursor <cursoragent@cursor.com>

.playwright-mcp/console-2026-02-12T09-06-28-438Z.log

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+[    7988ms] [ERROR] Failed to load resource: the server responded with a status of 404 (Not Found) @ http://localhost:5173/favicon.ico:0