docs: Document Docker build optimization (914MB → 27KB)

Added Docker build context optimization details to Architecture Overview:
- 33,389× smaller build context (914.39MB → 27.39KB)
- 89% faster context transfer (14.3s → 1.6s)
- 36% faster total builds (267.6s → 170.8s)
- Key exclusion patterns documented
- Commit reference for future context

.github/copilot-instructions.md

@@ -915,6 +915,16 @@ When you have high-resolution data (1 minute), use it immediately. Arbitrary del
 
 **Data Flow:** TradingView → n8n webhook → Next.js API → Drift Protocol (Solana DEX) → Real-time monitoring → Auto-exit
 
+**Docker Build Optimization (Dec 17, 2025):**
+- **Build context:** 914.39 MB → 27.39 KB (33,389× smaller)
+- **Context transfer:** 14.3s → 1.6s (89% faster transfer)
+- **Total build time:** 267.6s → 170.8s (36% faster builds)
+- **Key exclusions:** node_modules (688MB), Python venvs (100MB+), cluster data (143MB), CSV files
+- **Typical rebuild:** ~60-90s with layer caching (vs 267s before)
+- **Critical patterns in .dockerignore:** `**/node_modules`, `.venv/`, `cluster/.venv/`, `*.csv`, `cluster/chunks/`
+- **Why it matters:** Faster CI/CD, less disk I/O, quicker developer iteration
+- **Commit:** ce56a54 (Dec 17, 2025)
+
 **CRITICAL: RPC Provider Choice**
 - **MUST use Alchemy RPC** (https://solana-mainnet.g.alchemy.com/v2/YOUR_API_KEY)
 - **DO NOT use Helius free tier** - causes catastrophic rate limiting (239 errors in 10 minutes)