feat(backends): multi-backend intelligence layer — LLM + Agent backends, persona-loading agents, honest CLI commands

Add IntelligenceBackend abstraction with two categories:
- LLMBackend (OllamaLocal, OllamaCloud): CI runs tool loop, provides tools, constructs prompts
- AgentBackend (Opencode): agent runs own tool loop, CI serializes request

Refactor all 18 agents from hardcoded stubs to persona loaders that delegate
to the active backend or fail honestly when no backend is available.

Refactor OrchestratorAgent.executeStage() from monolithic switch to agent
delegation via STAGE_AGENT_MAP for intelligent stages (research, plan, execute,
verify), with mechanical stages (specify, clarify, complete) staying inline.

Wire CLI commands with --backend flag and auto-detection (opencode →
ollama-local → ollama-cloud). Harden rollback/ship with real git operations.
No command returns fake success.

src/agents/executor.ts

@@ -3,17 +3,26 @@ import { BaseAgent, AgentContext, AgentResult } from "./base.js";
 export class ExecutorAgent extends BaseAgent {
   readonly name = "executor";
   readonly description = "Executes plan tasks autonomously. Never pauses for checkpoints.";
+  readonly workflow = "execute";
 
   async execute(context: AgentContext): Promise<AgentResult> {
-    this.log("Executing tasks...");
     const start = Date.now();
+    this.log("Executing tasks...");
+    if (context.backend) {
+      const result = await this.executeViaBackend(
+        context,
+        `Execute implementation for stage ${context.stage}, phase ${context.phase}. Specification: ${context.specification}`
+      );
+      return { ...result, duration_ms: Date.now() - start };
+    }
     return {
-      success: true,
-      output: "Tasks executed",
+      success: false,
+      output: "Execution requires an intelligence backend. Configure one with: ci init --backend",
       artifacts_created: [],
       decisions: 0,
       escalations: 0,
       duration_ms: Date.now() - start,
+      error: "No intelligence backend available",
     };
   }
 }