docs: Add zero-downtime changes guide - stop unnecessary rebuilds

PROBLEM: Rebuilding container 4-6 times per session when most changes don't need it
- Every rebuild: 40-70 seconds downtime
- Recent session: 200 seconds downtime that could've been 50 seconds
- Rebuilding for documentation (should be git only)
- Rebuilding for n8n workflows (should be manual import)
- Rebuilding for ENV changes (should be restart only)

SOLUTION: Created comprehensive guide on what actually needs rebuilds

ZERO DOWNTIME (just commit):
- Documentation (.md files)
- Workflows (.json, .pinescript)
- Hot-reload endpoints (roadmap reload)

RESTART ONLY (5-10 seconds):
- ENV variable changes (.env)
- Database schema (prisma migrate + generate)

REBUILD REQUIRED (40-70 seconds):
- Code changes (.ts, .tsx, .js)
- Dependencies (package.json)
- Dockerfile changes

SMART BATCHING:
- Group multiple code changes into ONE rebuild
- Example: 6 fixes → 1 rebuild = 50s total (not 6× rebuilds = 300s)

CREATED FILES:
- docs/ZERO_DOWNTIME_CHANGES.md (comprehensive guide with examples)
- Updated copilot-instructions.md (quick decision matrix)

EXPECTED IMPACT:
- 60-80% reduction in rebuild frequency
- 60-80% reduction in downtime per session
- Better workflow: batch changes, test together, deploy once

User was right: We were rebuilding WAY too often unnecessarily ✅

.github/copilot-instructions.md

@@ -571,6 +571,50 @@ docker logs trading-bot-v4 | grep "Server starting" | head -1
 
 **DO NOT use:** `docker compose build trading-bot` in foreground - one network hiccup kills 60s of work
 
+### When to Actually Rebuild vs Restart vs Nothing
+
+**⚠️ CRITICAL: Stop rebuilding unnecessarily - costs 40-70 seconds downtime per rebuild**
+
+**See `docs/ZERO_DOWNTIME_CHANGES.md` for complete guide**
+
+**Quick Decision Matrix:**
+
+| Change Type | Action | Downtime | When |
+|------------|--------|----------|------|
+| Documentation (`.md`) | **NONE** | 0s | Just commit and push |
+| Workflows (`.json`, `.pinescript`) | **NONE** | 0s | Import manually to TradingView/n8n |
+| ENV variables (`.env`) | **RESTART** | 5-10s | `docker compose restart trading-bot` |
+| Database schema | **MIGRATE + RESTART** | 10-15s | `prisma migrate + restart` |
+| Code (`.ts`, `.tsx`, `.js`) | **REBUILD** | 40-70s | TypeScript must recompile |
+| Dependencies (`package.json`) | **REBUILD** | 40-70s | npm install required |
+
+**Smart Batching Strategy:**
+- **DON'T:** Rebuild after every single code change (6× rebuilds = 6 minutes downtime)
+- **DO:** Batch related changes together (6 fixes → 1 rebuild = 50 seconds total)
+
+**Example (GOOD):**
+```bash
+# 1. Make multiple code changes
+vim lib/trading/position-manager.ts
+vim app/api/trading/execute/route.ts
+vim lib/notifications/telegram.ts
+
+# 2. Commit all together
+git add -A && git commit -m "fix: Multiple improvements"
+
+# 3. ONE rebuild for everything
+docker compose build trading-bot
+docker compose up -d --force-recreate trading-bot
+
+# Total: 50 seconds (not 150 seconds)
+```
+
+**Recent Mistakes to Avoid (Nov 27, 2025):**
+- ❌ Rebuilt for documentation updates (should be git commit only)
+- ❌ Rebuilt for n8n workflow changes (should be manual import)
+- ❌ Rebuilt 4 times for 4 code changes (should batch into 1 rebuild)
+- ✅ Result: 200 seconds downtime that could have been 50 seconds
+
 ### Docker Cleanup After Builds
 
 **CRITICAL: Prevent disk full issues from build cache accumulation**