feat(js): add qdrant vector database client

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Fixes #273.

This PR adds Qdrant support to the JavaScript vector database package without using any Qdrant npm package. The client talks to Qdrant through the REST API directly.

Changes:

• adds a Qdrant vector DB client exported from @arakoodev/edgechains.js/vector-db
• supports collection creation, point upsert, point retrieval, vector search with filters, and point deletion
• supports QDRANT_URL and QDRANT_API_KEY environment variables
• adds mocked-fetch tests for the Qdrant REST requests and error handling
• adds a qdrant-vector-search example with JSONNet config

Verification:

• bun run build
• bun test src/vector-db/src/tests/qdrant/qdrant.test.ts

/claim #273

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