feat(agent): add human-like delay between block replies

Adds `agent.humanDelay` config option to create natural rhythm between
streamed message bubbles. When enabled, introduces a random delay
(default 800-2500ms) between block replies, making multi-message
responses feel more like natural human texting.

Config example:
```json
{
  "agent": {
    "blockStreamingDefault": "on",
    "humanDelay": {
      "enabled": true,
      "minMs": 800,
      "maxMs": 2500
    }
  }
}
```

- First message sends immediately
- Subsequent messages wait a random delay before sending
- Works with iMessage, Signal, and Discord providers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/agents/identity.ts

@@ -1,4 +1,8 @@
-import type { ClawdbotConfig, IdentityConfig } from "../config/config.js";
+import type {
+  ClawdbotConfig,
+  HumanDelayConfig,
+  IdentityConfig,
+} from "../config/config.js";
 import { resolveAgentConfig } from "./agent-scope.js";
 
 const DEFAULT_ACK_REACTION = "👀";
@@ -72,3 +76,17 @@ export function resolveEffectiveMessagesConfig(
     responsePrefix: resolveResponsePrefix(cfg, agentId),
   };
 }
+
+export function resolveHumanDelayConfig(
+  cfg: ClawdbotConfig,
+  agentId: string,
+): HumanDelayConfig | undefined {
+  const defaults = cfg.agents?.defaults?.humanDelay;
+  const overrides = resolveAgentConfig(cfg, agentId)?.humanDelay;
+  if (!defaults && !overrides) return undefined;
+  return {
+    mode: overrides?.mode ?? defaults?.mode,
+    minMs: overrides?.minMs ?? defaults?.minMs,
+    maxMs: overrides?.maxMs ?? defaults?.maxMs,
+  };
+}