feat(health): migrate VERSION file to merkwerk integration (#83)

- Replace read_version() with merkwerk.get_health_info()
- Health endpoint now returns content_hash, vcs_info, source tracking
- Add merkwerk_integrated feature flag
- Enhanced startup logs with content-hash and VCS info
- Maintain backward compatibility with version field
- lua51 compatible integration for OpenBSD deployment

Migration from static VERSION file to dynamic merkwerk version tracking.
Health endpoint now provides rich metadata for debugging and monitoring.

Resolves DAW/furt#83

src/main.lua

@@ -13,23 +13,29 @@ 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 "?.?.?"
+local function get_version_info()
+    -- Load merkwerk integration
+    local success, merkwerk = pcall(require, "integrations.lua-api")
+    if not success then
+        print("WARNING: merkwerk integration not available, using fallback")
+        return {
+            service = "furt-lua",
+            version = "?.?.?",
+            content_hash = "unknown",
+            vcs_info = { type = "none", hash = "", branch = "" },
+            source = "fallback-no-merkwerk"
+        }
     end
 
-    local version = file:read("*line")
-    file:close()
+    -- Get merkwerk health info
+    local health_info = merkwerk.get_health_info()
 
-    if not version or version:match("^%s*$") then
-        print("WARNING: VERSION file is empty or contains only whitespace")
-        return "?.?.?"
+    -- Ensure compatibility with old VERSION-only expectations
+    if not health_info.version then
+        health_info.version = "?.?.?"
     end
 
-    return version:match("^%s*(.-)%s*$") -- trim whitespace
+    return health_info
 end
 
 -- HTTP-Server Module
@@ -243,10 +249,12 @@ function FurtServer:start()
         error("Failed to bind to " .. self.host .. ":" .. self.port)
     end
 
-    local version = read_version()
+    local version_info = get_version_info()
 
     print(string.format("Furt HTTP-Server started on %s:%d", self.host, self.port))
-    print("Version: " .. version)
+    print("Version: " .. version_info.version .. " (merkwerk)")
+    print("Content-Hash: " .. (version_info.content_hash or "unknown"))
+    print("VCS: " .. (version_info.vcs_info and version_info.vcs_info.hash or "none"))
     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")
@@ -267,16 +275,20 @@ local server = FurtServer:new()
 
 -- Public routes (no authentication required)
 server:add_route("GET", "/health", function(request, server)
-    local version = read_version()
+    local version_info = get_version_info()
     local response_data = {
         status = "healthy",
-        service = "furt-lua",
-        version = version,
+        service = version_info.service or "furt-lua",
+        version = version_info.version,
+        content_hash = version_info.content_hash,
+        vcs_info = version_info.vcs_info,
         timestamp = os.time(),
+        source = version_info.source,
         features = {
             smtp_configured = config.mail and config.mail.username ~= nil,
             auth_enabled = true,
-            rate_limiting = true
+            rate_limiting = true,
+            merkwerk_integrated = version_info.source == "merkwerk"
         }
     }
     return server:create_response(200, response_data, nil, nil, request)