feat: Phase 3 — extract panel modules from app.js (Refs #422)

Create 6 panel modules under modules/panels/ plus supporting core
infrastructure (state.js, theme.js, ticker.js). Each panel:
  - Exports init(scene, state, theme) and update(elapsed, delta)
  - Uses NEXUS.theme for all colors/fonts (no inline hex codes)
  - Reads from state.js (no direct API calls)
  - Subscribes to ticker for animation

Panel modules:
  panels/heatmap.js       — Commit heatmap floor overlay (DATA-TETHERED)
  panels/agent-board.js   — Agent status holographic board (REAL)
  panels/dual-brain.js    — Dual-brain panel (HONEST-OFFLINE)
  panels/lora-panel.js    — LoRA adapter panel (HONEST-OFFLINE)
  panels/sovereignty.js   — Sovereignty meter arc gauge (REAL manual)
  panels/earth.js         — Holographic Earth, activity-tethered (DATA-TETHERED)

Core infrastructure (consumed by panels):
  core/state.js   — shared reactive data bus
  core/theme.js   — NEXUS.theme design system
  core/ticker.js  — single RAF loop + subscribe/unsubscribe API

All files pass `node --check`. app.js unchanged.

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

modules/core/theme.js

@@ -0,0 +1,56 @@
+// modules/core/theme.js — Visual design system for the Nexus
+// All colors, fonts, line weights, and glow params live here.
+// No module may use inline hex codes — all visual constants come from NEXUS.theme.
+
+export const NEXUS = {
+  theme: {
+    // Core palette
+    bg:                0x000008,
+    accent:            0x4488ff,
+    accentStr:         '#4488ff',
+    starCore:          0xffffff,
+    starDim:           0x8899cc,
+    constellationLine: 0x334488,
+
+    // Agent status colors (hex strings for canvas, hex numbers for THREE)
+    agentWorking:      '#00ff88',
+    agentWorkingHex:   0x00ff88,
+    agentIdle:         '#4488ff',
+    agentIdleHex:      0x4488ff,
+    agentDormant:      '#334466',
+    agentDormantHex:   0x334466,
+    agentDead:         '#ff4444',
+    agentDeadHex:      0xff4444,
+
+    // Sovereignty meter colors
+    sovereignHigh:     '#00ff88',   // score >= 80
+    sovereignHighHex:  0x00ff88,
+    sovereignMid:      '#ffcc00',   // score >= 40
+    sovereignMidHex:   0xffcc00,
+    sovereignLow:      '#ff4444',   // score < 40
+    sovereignLowHex:   0xff4444,
+
+    // LoRA / training panel
+    loraAccent:        '#cc44ff',
+    loraAccentHex:     0xcc44ff,
+    loraActive:        '#00ff88',
+    loraInactive:      '#334466',
+
+    // Earth
+    earthOcean:        0x003d99,
+    earthLand:         0x1a5c2a,
+    earthAtm:          0x1144cc,
+    earthGlow:         0x4488ff,
+
+    // Panel chrome
+    panelBg:           'rgba(0, 6, 20, 0.90)',
+    panelBorder:       '#4488ff',
+    panelBorderFaint:  '#1a3a6a',
+    panelText:         '#ccd6f6',
+    panelDim:          '#556688',
+    panelVeryDim:      '#334466',
+
+    // Typography
+    fontMono:          '"Courier New", monospace',
+  },
+};