feat: Phase 9 — developer experience, extensibility, and community growth

New crates:
- quicproquo-bot: Bot SDK with polling API + JSON pipe mode
- quicproquo-kt: Key Transparency Merkle log (RFC 9162 subset)
- quicproquo-plugin-api: no_std C-compatible plugin vtable API
- quicproquo-gen: scaffolding tool (qpq-gen plugin/bot/rpc/hook)

Server features:
- ServerHooks trait wired into all RPC handlers (enqueue, fetch, auth,
  channel, registration) with plugin rejection support
- Dynamic plugin loader (libloading) with --plugin-dir config
- Delivery proof canary tokens (Ed25519 server signatures on enqueue)
- Key Transparency Merkle log with inclusion proofs on resolveUser

Core library:
- Safety numbers (60-digit HMAC-SHA256 key verification codes)
- Verifiable transcript archive (CBOR + ChaCha20-Poly1305 + hash chain)
- Delivery proof verification utility
- Criterion benchmarks (hybrid KEM, MLS, identity, sealed sender, padding)

Client:
- /verify REPL command for out-of-band key verification
- Full-screen TUI via Ratatui (feature-gated --features tui)
- qpq export / qpq export-verify CLI subcommands
- KT inclusion proof verification on user resolution

Also: ROADMAP Phase 9 added, bot SDK docs, server hooks docs,
crate-responsibilities updated, example plugins (rate_limit, logging).

crates/quicproquo-client/Cargo.toml

@@ -12,6 +12,7 @@ path = "src/main.rs"
 [dependencies]
 quicproquo-core  = { path = "../quicproquo-core" }
 quicproquo-proto = { path = "../quicproquo-proto" }
+quicproquo-kt    = { path = "../quicproquo-kt" }
 openmls_rust_crypto = { workspace = true }
 
 # Serialisation + RPC
@@ -38,6 +39,7 @@ thiserror     = { workspace = true }
 sha2          = { workspace = true }
 argon2        = { workspace = true }
 chacha20poly1305 = { workspace = true }
+ciborium      = { workspace = true }
 zeroize       = { workspace = true }
 quinn         = { workspace = true }
 quinn-proto   = { workspace = true }
@@ -65,10 +67,16 @@ mdns-sd = { version = "0.12", optional = true }
 # Optional P2P transport for direct node-to-node messaging.
 quicproquo-p2p = { path = "../quicproquo-p2p", optional = true }
 
+# Optional TUI dependencies (Ratatui full-screen interface).
+ratatui = { version = "0.29", optional = true, default-features = false, features = ["crossterm"] }
+crossterm = { version = "0.28", optional = true }
+
 [features]
 # Enable mesh-mode features: mDNS local peer discovery + P2P transport.
 # Build: cargo build -p quicproquo-client --features mesh
 mesh = ["dep:mdns-sd", "dep:quicproquo-p2p"]
+# Enable full-screen Ratatui TUI: cargo build -p quicproquo-client --features tui
+tui = ["dep:ratatui", "dep:crossterm"]
 
 [dev-dependencies]
 dashmap       = { workspace = true }