feat(persistence): add SQLite persistence for conversation state and models

Implement comprehensive SQLite-based persistence layer:

- PersistenceManager with full CRUD operations for conversations
- Save/load conversation history with project isolation
- Persist reservoir computing state across sessions
- Store trained MLP weights with accuracy tracking
- Configuration persistence
- Database utilities (vacuum, size checking)
- Full test coverage (7 tests, all passing)

Schema includes:
- conversations table (indexed by project and timestamp)
- reservoir_states table (per-project state)
- model_weights table (versioned model storage)
- metadata and config tables

Features:
- Transaction safety
- Query parameterization (SQL injection safe)
- Efficient indexing for common queries
- In-memory database support for testing
- Graceful handling of missing data

Dependencies added:
- rusqlite 0.31 (bundled SQLite)
- lazy_static 1.4 (global state)
- rand 0.8 (for training)
- proptest 1.4 (dev dependency for future property tests)

Default feature: persistence enabled by default for production use
Can be disabled with --no-default-features for minimal builds

Stats: 612 lines of persistence code + tests
All tests passing: cargo test --features persistence persistence

Author: claude

Cargo.toml

@@ -15,6 +15,11 @@ rust-version = "1.75"
 # Core dependencies - keeping minimal for Bronze RSR compliance
 serde = { version = "1.0", features = ["derive"] }
 serde_json = { version = "1.0" }
+lazy_static = "1.4"
+rand = "0.8"
+
+# Persistence
+rusqlite = { version = "0.31", features = ["bundled"], optional = true }
 
 # Optional dependencies for future phases
 tokio = { version = "1.35", features = ["rt", "macros", "sync"], optional = true }
@@ -23,11 +28,14 @@ reqwest = { version = "0.11", features = ["json"], optional = true }
 [dev-dependencies]
 # Test dependencies
 criterion = "0.5"
+proptest = "1.4"
 
 [features]
-default = []
+default = ["persistence"]
 # Network features disabled by default for offline-first
 network = ["tokio", "reqwest"]
+# Persistence (enabled by default for production use)
+persistence = ["rusqlite"]
 # Phase 2+ features
 reservoir = []
 rag = []

src/lib.rs

@@ -30,6 +30,7 @@ pub mod context;
 pub mod expert;
 pub mod mlp;
 pub mod orchestrator;
+pub mod persistence;
 pub mod reservoir;
 pub mod router;
 pub mod snn;