multi-agent research: parallel LLM-powered investigation

new research tool spawns 3-25 micro-agents (ministral-3b) in
parallel via futures::join_all. each agent gets its own Mistral
conversation with full tool access.

recursive spawning up to depth 4 — agents can spawn sub-agents.
research sessions persisted in SQLite (survive reboots).
thread UX: 🔍 reaction, per-agent progress posts, ✅ when done.

cost: ~$0.03 per research task (20 micro-agents on ministral-3b).

Cargo.toml

@@ -37,3 +37,4 @@ reqwest = { version = "0.12", default-features = false, features = ["rustls-tls"
 uuid = { version = "1", features = ["v4"] }
 base64 = "0.22"
 rusqlite = { version = "0.32", features = ["bundled"] }
+futures = "0.3"