fix(json): add multi-platform JSON library compatibility

- Add flexible JSON detection (cjson preferred, dkjson fallback)
- Update main.lua and mail.lua with found_cjson detection
- Update start.sh to check both JSON libraries
- Enables furt to run on Arch Linux without manual patches
- Maintains API compatibility with existing cjson usage

Fixes #108

scripts/start.sh

@@ -59,10 +59,12 @@ $LUA_COMMAND -e "require('socket')" 2>/dev/null || {
     exit 1
 }
 
-$LUA_COMMAND -e "require('cjson')" 2>/dev/null || {
-    echo -e "${RED}Error: lua-cjson not found${NC}"
+# JSON library check (cjson preferred, dkjson fallback)
+if ! ($LUA_COMMAND -e "require('cjson')" 2>/dev/null || $LUA_COMMAND -e "require('dkjson')" 2>/dev/null); then
+    echo -e "${RED}Error: No JSON library found${NC}"
+    echo "Install lua-cjson or lua-dkjson"
     exit 1
-}
+fi
 
 cd "$PROJECT_DIR"
 

src/main.lua

@@ -3,7 +3,10 @@
 -- Dragons@Work Digital Sovereignty Project
 
 local socket = require("socket")
-local cjson = require("cjson")
+local found_cjson, cjson = pcall(require, 'cjson')
+if not found_cjson then
+    cjson = require('dkjson')
+end
 
 -- Load modules
 local Auth = require("src.auth")

src/routes/mail.lua

@@ -3,7 +3,10 @@
 -- API-Key determines mail configuration and recipient
 -- Dragons@Work Digital Sovereignty Project
 
-local cjson = require("cjson")
+local found_cjson, cjson = pcall(require, 'cjson')
+if not found_cjson then
+    cjson = require('dkjson')
+end
 
 local MailRoute = {}