feat: AgentDB.getController() — add wasmVectorSearch + safe null for rvfOptimizer

[sparkling]

Problem

`AgentDB.getController('wasmVectorSearch')` throws `Unknown controller` because there is no case for it. AgentDBService constructs its own private `WASMVectorSearch` instance, creating a duplicate that is invisible to ControllerRegistry.

Similarly, `getController('rvfOptimizer')` throws, preventing AgentDBService from attempting delegation.

Proposed Fix

1. Add `wasmVectorSearch` case to `getController()` with lazy singleton initialization
2. Add `rvfOptimizer` case returning null (safe no-op, prevents throw on delegation attempt)
3. Update AgentDBService Phase 1 init to delegate `wasmVectorSearch` through `getController()`

ADR Reference

ADR-0076 Track B controller-bridge analysis