docs: Add comprehensive Docker troubleshooting guide

DOCKER_SETUP.md

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+# Docker Setup Documentation
+
+## Issue: Infinite Restart Loop
+
+This document explains the Docker configuration issues that caused infinite restart loops and how they were resolved.
+
+## Problems Identified
+
+### 1. Import Path Issue
+**Location:** `src/common/color.js:3`
+
+**Problem:** The import path was pointing to `../../themes/index.js` (root level) but themes directory was moved to `src/themes/`
+
+**Solution:**
+```javascript
+// Before
+import { themes } from "../../themes/index.js";
+
+// After
+import { themes } from "../themes/index.js";
+```
+
+### 2. Missing Dependencies
+**Location:** `src/package.json`
+
+**Problem:** The src/package.json only had devDependencies, missing all runtime dependencies needed by the application.
+
+**Solution:** Added production dependencies:
+```json
+"dependencies": {
+  "axios": "^1.13.1",
+  "dotenv": "^17.2.3",
+  "emoji-name-map": "^2.0.3",
+  "github-username-regex": "^1.0.0",
+  "word-wrap": "^1.2.5"
+}
+```
+
+### 3. Wrong Docker Build Context
+**Location:** `docker-compose.yml`
+
+**Problem:** Build context was set to `./src` but the actual server file (`express.js`) and `api/` directory are at the root level.
+
+**Solution:**
+```yaml
+# Before
+build:
+  context: ./src
+  dockerfile: Dockerfile
+
+# After
+build:
+  context: .
+  dockerfile: Dockerfile
+```
+
+### 4. Wrong Entry Point
+**Location:** `Dockerfile` CMD instruction
+
+**Problem:** Container was trying to run `src/index.js` which only exports modules, not the actual Express server.
+
+**Solution:**
+```dockerfile
+# Before
+CMD ["node", "index.js"]
+
+# After
+CMD ["node", "express.js"]
+```
+
+### 5. Node Version Mismatch
+**Location:** `Dockerfile`
+
+**Problem:** Dockerfile used Node 18, but `package.json` requires Node >=22
+
+**Solution:**
+```dockerfile
+# Before
+FROM node:18-alpine AS base
+
+# After
+FROM node:22-alpine AS base
+```
+
+### 6. Husky Prepare Script
+**Location:** `Dockerfile` npm install step
+
+**Problem:** The `prepare` script tries to run `husky` (git hooks) during Docker build, which fails and isn't needed in containers.
+
+**Solution:**
+```dockerfile
+npm ci --omit=dev --ignore-scripts
+```
+
+## Final Working Configuration
+
+### Dockerfile Structure
+```dockerfile
+FROM node:22-alpine AS base
+
+# Dependencies stage - installs only production dependencies
+FROM base AS deps
+RUN apk add --no-cache libc6-compat
+WORKDIR /app
+COPY package.json yarn.lock* package-lock.json* pnpm-lock.yaml* .npmrc* ./
+RUN npm ci --omit=dev --ignore-scripts
+
+# Builder stage - prepares application files
+FROM base AS builder
+WORKDIR /app
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+
+# Runner stage - production image
+FROM base AS runner
+WORKDIR /app
+ENV NODE_ENV=production
+COPY --from=builder /app/package.json ./package.json
+COPY --from=builder /app/node_modules ./node_modules
+COPY --from=builder /app/src ./src
+COPY --from=builder /app/api ./api
+COPY --from=builder /app/themes ./themes
+COPY --from=builder /app/express.js ./express.js
+
+EXPOSE 3000
+CMD ["node", "express.js"]
+```
+
+## Testing the Setup
+
+### Start the container
+```bash
+docker compose up -d
+```
+
+### Check container status
+```bash
+docker ps --filter "name=github-readme-stats"
+```
+
+### View logs
+```bash
+docker logs github-readme-stats
+```
+
+Expected output:
+```
+[[email protected]] injecting env (0) from .env
+Server running on port 3000
+```
+
+### Test the API
+```bash
+curl "http://localhost:3000/api/?username=YOUR_GITHUB_USERNAME"
+```
+
+## Deployment Notes
+
+Before deploying to VPS:
+
+1. **Environment Variables:** Create a `.env` file with your GitHub token:
+   ```
+   PAT_1=your_github_personal_access_token
+   ```
+
+2. **Port Configuration:** Update `docker-compose.yml` if you need a different port:
+   ```yaml
+   ports:
+     - "8080:3000"  # Maps host port 8080 to container port 3000
+   ```
+
+3. **Domain Configuration:** Update Traefik labels in `docker-compose.yml`:
+   ```yaml
+   - "traefik.http.routers.github-readme-stats.rule=Host(`your-domain.com`)"
+   ```
+
+4. **SSL/TLS:** Ensure your Traefik setup has a valid cert resolver configured
+
+## Troubleshooting
+
+### Container keeps restarting
+```bash
+# Check logs immediately
+docker logs github-readme-stats --tail 50
+
+# Common issues:
+# - Missing dependencies: Check package.json
+# - Module not found: Check import paths
+# - Port conflicts: Check if port 3000 is available
+```
+
+### Port already in use
+```bash
+# Windows PowerShell
+Get-Process -Id (Get-NetTCPConnection -LocalPort 3000).OwningProcess
+Stop-Process -Id <PID> -Force
+
+# Linux/Mac
+lsof -ti:3000 | xargs kill -9
+```
+
+## File Structure
+```
+github-readme-stats/
+├── api/                    # API endpoints
+├── src/                    # Source code
+│   ├── common/            # Common utilities
+│   ├── cards/             # Card generators
+│   ├── fetchers/          # Data fetchers
+│   └── themes/            # Theme definitions
+├── themes/                 # Root themes (legacy)
+├── express.js             # Express server (entry point)
+├── Dockerfile             # Docker configuration
+├── docker-compose.yml     # Docker Compose setup
+└── package.json           # Dependencies
+```