docs(readme): add bundlejs size badge for core package #116

Job	Run time
Gate (skip full CI for version PRs?)	3s
🕵 Lint	12s
🧰 Build	31s
🔬 Test	29s
🌐 Test (DOM)	59s
💅 Format	18s
🧩 Workspace deps	15s
🔗 Doc links	8s
📖 Docs site (Blume)	1m 30s
🛡 Audit	12s
✅ Typecheck	1m 2s
📦 Pack validation	47s
📏 Bundle size	30s
CI complete	4s
	7m 0s

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