feat: add smart endpoint router

[yassine1234944-design]

Summary

• Adds SmartEndpointRouter for OpenAI, PaLM/Gemini-style, and Cohere deployments.
• Routes requests to the healthy deployment with the least token usage.
• Supports token limits, cooldown after 429/5xx failures, retries across deployments, and observability callbacks.
• Adds mocked tests for routing, cooldown retry behavior, and callback emission.

/claim #286

Validation

• npx.cmd -y prettier@3.2.5 --check src/ai/src/lib/smart-router/smartRouter.ts src/ai/src/tests/smartRouter.test.ts src/ai/src/index.ts
• npx.cmd -y vitest@2.0.3 run src/ai/src/tests/smartRouter.test.ts
• npx.cmd -y esbuild@0.20.2 src/ai/src/index.ts --bundle --external:* --platform=node --format=esm --outfile=$env:TEMP\edgechains-ai-router.mjs --log-level=error
• npx.cmd -p typescript@5.6.3 tsc -p tsconfig.json --emitDeclarationOnly --outDir

[github-actions]

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[yassine1234944-design]

I have read the Arakoo CLA Document and I hereby sign the CLA

[yassine1234944-design]

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