feat: add multimodal search and granular performance diagnostics

AGENTS.md

@@ -10,6 +10,9 @@ readiness without completed release gates and recorded evidence.
 - Production uses available GPU/hardware acceleration with reliable CPU fallback;
   the CPU-only rule is a VM testing constraint, not a product restriction.
 - Keep the Rust engine independent of the desktop shell; CLI and UI share its API.
+- Prefer established Rust crates and proven retrieval algorithms over custom
+  implementations. Keep platform adapters small, bound allocations and queues,
+  and measure performance before adding caches or changing ranking policies.
 - Use bounded work, explicit errors, versioned storage, and offline defaults.
 - Never substitute simulated embeddings for working semantic search.
 - Production semantic search must use Google EmbeddingGemma 2 as in DigUp.