feat: live agent status board — 3D floating holo-panels (#199)

Add five floating holographic panels arranged in a 135° semi-circle
behind the platform, one per agent (claude, gemini, kimi, groq, grok).
Each panel shows agent name, status (working/idle/dead) with a colour-
coded dot, current issue title, and PRs merged today.

Status data is fetched from /api/status.json every 30 seconds; the
stub JSON is committed so the scene works without a live backend.
Panel sprites float gently via the existing animation loop.

Fixes #199

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/status.json

@@ -0,0 +1,9 @@
+{
+  "agents": [
+    { "name": "claude",  "status": "working", "issue": "Live agent status board (#199)", "prs_today": 3 },
+    { "name": "gemini",  "status": "idle",    "issue": null,                              "prs_today": 1 },
+    { "name": "kimi",    "status": "working", "issue": "Portal system YAML registry (#5)", "prs_today": 2 },
+    { "name": "groq",    "status": "idle",    "issue": null,                              "prs_today": 0 },
+    { "name": "grok",    "status": "dead",    "issue": null,                              "prs_today": 0 }
+  ]
+}