feat(core): implement file-based API versioning system (DAW/furt#83)

- Add VERSION file in repository root
- Add read_version() function with error handling
- Update /health endpoint to show file-based version
- Add version display during server startup
- Fallback to ?.?.? when VERSION file unreadable

Enables deployment tracking across dev/test/prod environments

VERSION

@@ -0,0 +1 @@
+0.1.1

src/main.lua

@@ -13,6 +13,25 @@ local AuthRoute = require("src.routes.auth")
 -- Load configuration
 local config = require("config.server")
 
+-- Read version from VERSION file
+local function read_version()
+    local file, err = io.open("VERSION", "r")
+    if not file then
+        print("WARNING: Could not read VERSION file: " .. (err or "unknown error"))
+        return "?.?.?"
+    end
+
+    local version = file:read("*line")
+    file:close()
+
+    if not version or version:match("^%s*$") then
+        print("WARNING: VERSION file is empty or contains only whitespace")
+        return "?.?.?"
+    end
+
+    return version:match("^%s*(.-)%s*$") -- trim whitespace
+end
+
 -- HTTP-Server Module
 local FurtServer = {}
 
@@ -224,7 +243,10 @@ function FurtServer:start()
         error("Failed to bind to " .. self.host .. ":" .. self.port)
     end
 
+    local version = read_version()
+
     print(string.format("Furt HTTP-Server started on %s:%d", self.host, self.port))
+    print("Version: " .. version)
     print("API-Key authentication: ENABLED")
     print("Rate limiting: ENABLED (60 req/hour per API key, 100 req/hour per IP)")
     print("CORS enabled for configured origins")
@@ -245,10 +267,11 @@ local server = FurtServer:new()
 
 -- Public routes (no authentication required)
 server:add_route("GET", "/health", function(request, server)
+    local version = read_version()
     local response_data = {
         status = "healthy",
         service = "furt-lua",
-        version = "1.1.0",
+        version = version,
         timestamp = os.time(),
         features = {
             smtp_configured = config.mail and config.mail.username ~= nil,
@@ -276,7 +299,7 @@ if os.getenv("ENABLE_TEST_ENDPOINT") == "true" then
 
         return server:create_response(200, response_data, nil, nil, request)
     end)
-    print("⚠️  Test endpoint enabled (development mode)")
+    print("[WARN] Test endpoint enabled (development mode)")
 end
 
 -- Protected routes (require authentication)