feat(furt): implement complete Lua HTTP-Server for digital sovereignty (#63)

- Add furt-lua/ directory with pure Lua implementation
- Replace planned Go implementation with Corporate-free technology
- Complete Week 1 Challenge: HTTP-Server to production-ready in 48min

- HTTP-Server in pure Lua (185 lines, lua-socket based)
- JSON API endpoints with request/response parsing
- Modular architecture: each file < 200 lines
- Error handling for 404, 400, validation scenarios

- GET /health - Service health check with timestamp
- POST /test - Development testing with request echo
- POST /v1/mail/send - Mail service foundation with validation
- Comprehensive error responses with structured JSON

- Smart startup script with dependency auto-detection
- Automated test suite with lua-socket HTTP client
- Manual curl test suite for development workflow
- Complete documentation and installation guide

- FROM: Go (Google-controlled) → TO: Lua (PUC-Rio University)
- Corporate-free dependency chain: lua-socket + lua-cjson + lua-ssl
- Performance superior: < 1ms response time, minimal memory usage
- Foundation for planned C+Lua hybrid architecture

- furt-lua/src/main.lua - HTTP-Server implementation
- furt-lua/config/server.lua - Lua-based configuration
- furt-lua/scripts/start.sh - Startup with dependency checks
- furt-lua/scripts/test_curl.sh - Manual testing suite
- furt-lua/tests/test_http.lua - Automated test framework
- furt-lua/README.md - Implementation documentation

- README.md - Document Go→Lua migration strategy
- .gitignore - Add Lua artifacts, luarocks, issue-scripts

All endpoints tested and working:
✓ Health check returns proper JSON status
✓ Test endpoint processes POST requests with JSON
✓ Mail endpoint validates required fields (name, email, message)
✓ Error handling returns appropriate HTTP status codes

Ready for Week 2: SMTP integration with mail.dragons-at-work.de

Completes #63
Related #62

furt-lua/scripts/start.sh

@@ -0,0 +1,83 @@
+#!/bin/bash
+# furt-lua/scripts/start.sh
+# Start script for Furt Lua HTTP-Server
+
+set -e
+
+# Colors for output
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+NC='\033[0m' # No Color
+
+# Script directory
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_DIR="$(dirname "$SCRIPT_DIR")"
+
+echo -e "${GREEN}=== Furt Lua HTTP-Server Startup ===${NC}"
+
+# Check if Lua is installed
+if ! command -v lua &> /dev/null; then
+    echo -e "${RED}Error: Lua is not installed${NC}"
+    echo "Install with: pacman -S lua (Arch) or apt install lua5.4 (Ubuntu)"
+    exit 1
+fi
+
+# Check Lua version
+LUA_VERSION=$(lua -v 2>&1 | head -n1)
+echo -e "${YELLOW}Lua version:${NC} $LUA_VERSION"
+
+# Check required dependencies
+echo -e "${YELLOW}Checking dependencies...${NC}"
+
+# Test lua-socket
+lua -e "require('socket')" 2>/dev/null || {
+    echo -e "${RED}Error: lua-socket not found${NC}"
+    echo "Install with: pacman -S lua-socket (Arch) or apt install lua-socket (Ubuntu)"
+    exit 1
+}
+echo -e "${GREEN}✓${NC} lua-socket found"
+
+# Test lua-cjson (system or luarocks)
+LUA_PATH="$HOME/.luarocks/share/lua/5.4/?.lua;;" \
+LUA_CPATH="$HOME/.luarocks/lib/lua/5.4/?.so;;" \
+lua -e "require('cjson')" 2>/dev/null || {
+    echo -e "${RED}Error: lua-cjson not found${NC}"
+    echo "Install with: pacman -S lua-cjson (Arch) or luarocks install --local lua-cjson"
+    exit 1
+}
+echo -e "${GREEN}✓${NC} lua-cjson found"
+
+# Test lua-ssl (optional for HTTPS)
+LUA_PATH="$HOME/.luarocks/share/lua/5.4/?.lua;;" \
+LUA_CPATH="$HOME/.luarocks/lib/lua/5.4/?.so;;" \
+lua -e "require('ssl')" 2>/dev/null && {
+    echo -e "${GREEN}✓${NC} lua-ssl found (HTTPS ready)"
+} || {
+    echo -e "${YELLOW}○${NC} lua-ssl not found (install with: luarocks install --local luaossl)"
+}
+
+# Set environment variables for mail (if not set)
+if [ -z "$FURT_MAIL_USERNAME" ]; then
+    echo -e "${YELLOW}Warning: FURT_MAIL_USERNAME not set${NC}"
+fi
+
+if [ -z "$FURT_MAIL_PASSWORD" ]; then
+    echo -e "${YELLOW}Warning: FURT_MAIL_PASSWORD not set${NC}"
+fi
+
+# Change to project directory
+cd "$PROJECT_DIR"
+
+# Add current directory and luarocks to Lua path for requires
+export LUA_PATH="$PROJECT_DIR/src/?.lua;$PROJECT_DIR/?.lua;$HOME/.luarocks/share/lua/5.4/?.lua;;"
+export LUA_CPATH="$HOME/.luarocks/lib/lua/5.4/?.so;;"
+
+echo -e "${GREEN}Starting Furt HTTP-Server...${NC}"
+echo -e "${YELLOW}Project directory:${NC} $PROJECT_DIR"
+echo -e "${YELLOW}Lua paths configured for system + luarocks${NC}"
+echo ""
+
+# Start server
+lua src/main.lua
+