feat: scaffold ECC 2.0 Rust TUI — agentic IDE control plane

Initial scaffold for ECC 2.0, a terminal-native agentic IDE built with
Ratatui. Compiles to a 3.4MB single binary.

Core modules:
- Session manager with SQLite-backed state store
- TUI dashboard with split-pane layout (sessions, output, metrics)
- Worktree orchestration (auto-create per agent session)
- Observability with tool call risk scoring
- Inter-agent communication via SQLite mailbox
- Background daemon with heartbeat monitoring
- CLI with start/stop/sessions/status/daemon subcommands

Tech stack: Rust + Ratatui + Crossterm + Tokio + rusqlite + git2 + clap

ecc2/src/session/mod.rs

@@ -0,0 +1,59 @@
+pub mod daemon;
+pub mod manager;
+pub mod store;
+
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use std::fmt;
+use std::path::PathBuf;
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Session {
+    pub id: String,
+    pub task: String,
+    pub agent_type: String,
+    pub state: SessionState,
+    pub worktree: Option<WorktreeInfo>,
+    pub created_at: DateTime<Utc>,
+    pub updated_at: DateTime<Utc>,
+    pub metrics: SessionMetrics,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+pub enum SessionState {
+    Pending,
+    Running,
+    Idle,
+    Completed,
+    Failed,
+    Stopped,
+}
+
+impl fmt::Display for SessionState {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            SessionState::Pending => write!(f, "pending"),
+            SessionState::Running => write!(f, "running"),
+            SessionState::Idle => write!(f, "idle"),
+            SessionState::Completed => write!(f, "completed"),
+            SessionState::Failed => write!(f, "failed"),
+            SessionState::Stopped => write!(f, "stopped"),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct WorktreeInfo {
+    pub path: PathBuf,
+    pub branch: String,
+    pub base_branch: String,
+}
+
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct SessionMetrics {
+    pub tokens_used: u64,
+    pub tool_calls: u64,
+    pub files_changed: u32,
+    pub duration_secs: u64,
+    pub cost_usd: f64,
+}