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/doc-writer.ts

@@ -3,17 +3,26 @@ import { BaseAgent, AgentContext, AgentResult } from "./base.js";
 export class DocWriterAgent extends BaseAgent {
   readonly name = "doc-writer";
   readonly description = "Autonomous documentation writer. No behavioral changes from Learnship.";
+  readonly workflow = "execute";
 
   async execute(context: AgentContext): Promise<AgentResult> {
-    this.log("Writing documentation...");
     const start = Date.now();
+    this.log("Writing documentation...");
+    if (context.backend) {
+      const result = await this.executeViaBackend(
+        context,
+        `Write documentation for phase ${context.phase}. Specification: ${context.specification}`
+      );
+      return { ...result, duration_ms: Date.now() - start };
+    }
     return {
-      success: true,
-      output: "Documentation written",
-      artifacts_created: ["DOCS.md"],
+      success: false,
+      output: "Documentation writing requires an intelligence backend.",
+      artifacts_created: [],
       decisions: 0,
       escalations: 0,
       duration_ms: Date.now() - start,
+      error: "No intelligence backend available",
     };
   }
 }