feat: implement orchestrator core (Rust)

Task 1.1: ✅ Cargo.toml with axum, rusqlite, matrix-sdk, serde, etc.
Task 1.2: ✅ Directory structure: src/core, src/adapters, src/integrations, src/api
Task 1.5: ✅ config.example.toml with full schema
Task 2.1: ✅ Data models: Agent, Task, Receipt, Artifact, TaskEvent
Task 2.2: ✅ Event Store: SQLite append-only with task/agent tables
Task 2.3: ✅ Task state machine: created→assigned→running→completed/failed
Task 2.4: ✅ Global task queue with priority ordering
Task 2.5: ✅ Background timeout checker
Task 2.6: ✅ Retry policy with configurable max_retries

Compiles clean (warnings only, no errors).
API handler stubs in place for Phase 2.

src/core/models.rs

@@ -0,0 +1,145 @@
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+
+// ─── Agent ───────────────────────────────────────────────────────
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, Hash)]
+#[serde(rename_all = "kebab-case")]
+pub enum AgentType {
+    OpenClaw,
+    ClaudeCode,
+    CodexCli,
+    Hermes,
+    Acp,
+    Shell,
+    Other(String),
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+#[serde(rename_all = "lowercase")]
+pub enum AgentStatus {
+    Online,
+    Offline,
+    Draining,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Agent {
+    pub agent_id: String,
+    pub agent_type: AgentType,
+    pub hostname: String,
+    pub capabilities: Vec<String>,
+    pub max_concurrency: u32,
+    pub current_tasks: u32,
+    pub status: AgentStatus,
+    pub last_heartbeat_at: DateTime<Utc>,
+    pub registered_at: DateTime<Utc>,
+    pub metadata: std::collections::HashMap<String, String>,
+}
+
+// ─── Task ────────────────────────────────────────────────────────
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+#[serde(rename_all = "lowercase")]
+pub enum TaskStatus {
+    Created,
+    Assigned,
+    Running,
+    Completed,
+    Failed,
+    AgentLost,
+    Cancelled,
+}
+
+impl TaskStatus {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            Self::Created => "created",
+            Self::Assigned => "assigned",
+            Self::Running => "running",
+            Self::Completed => "completed",
+            Self::Failed => "failed",
+            Self::AgentLost => "agent_lost",
+            Self::Cancelled => "cancelled",
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, PartialOrd, Ord)]
+#[serde(rename_all = "lowercase")]
+pub enum Priority {
+    Low,
+    Normal,
+    High,
+    Urgent,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Task {
+    pub task_id: String,
+    pub source: String,       // "forgejo:<repo>#<issue>"
+    pub task_type: String,    // "code", "review", "test", "deploy", "research"
+    pub priority: Priority,
+    pub status: TaskStatus,
+    pub assigned_agent_id: Option<String>,
+    pub requirements: String, // Issue body
+    pub labels: Vec<String>,
+    pub created_at: DateTime<Utc>,
+    pub assigned_at: Option<DateTime<Utc>>,
+    pub started_at: Option<DateTime<Utc>>,
+    pub completed_at: Option<DateTime<Utc>>,
+    pub retry_count: u32,
+    pub max_retries: u32,
+    pub timeout_seconds: u64,
+}
+
+// ─── Receipt ─────────────────────────────────────────────────────
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+#[serde(rename_all = "lowercase")]
+pub enum ReceiptStatus {
+    Completed,
+    Failed,
+    Partial,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+#[serde(rename_all = "lowercase")]
+pub enum ArtifactType {
+    Pr,
+    Commit,
+    File,
+    Comment,
+    Url,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Artifact {
+    pub artifact_type: ArtifactType,
+    pub url: Option<String>,
+    pub path: Option<String>,
+    pub description: Option<String>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Receipt {
+    pub task_id: String,
+    pub agent_id: String,
+    pub status: ReceiptStatus,
+    pub duration_seconds: u64,
+    pub summary: String,
+    pub artifacts: Vec<Artifact>,
+    pub error: Option<String>,
+}
+
+// ─── TaskEvent (event sourcing) ──────────────────────────────────
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TaskEvent {
+    pub event_id: String,
+    pub task_id: String,
+    pub event_type: String,
+    pub agent_id: Option<String>,
+    pub timestamp: DateTime<Utc>,
+    pub payload: serde_json::Value,
+}