Fix lock file: timestamp-based staleness, periodic refresh

- Lock file now contains a timestamp, refreshed every 0.5s
- Stale locks (>5s old) are ignored and cleaned up automatically
- Fixes: Aseprite crash leaving orphan lock, lock not cleaned on close
- Silent ignore still works for active instances

aniphallow.lua

@@ -1267,6 +1267,11 @@ local function removeLockFile()
     os.remove(LOCK_FILE)
 end
 
+local function refreshLockFile()
+    local lf = io.open(LOCK_FILE, "w")
+    if lf then lf:write(tostring(os.time())); lf:close() end
+end
+
 ----------------------------------------------------------------------
 -- Preview Window (primary window)
 ----------------------------------------------------------------------
@@ -1502,6 +1507,7 @@ openPreviewWindow = function()
         interval = 0.5,
         ontick = function()
             refreshSource()
+            refreshLockFile()
             pcall(function() previewDlg:repaint() end)
 
             -- Auto-detect file change
@@ -3273,14 +3279,21 @@ local function run()
         return
     end
     -- Check if already running via lock file - silently ignore
+    -- Lock file contains a timestamp; if older than 5 seconds, consider it stale
     local lockF = io.open(LOCK_FILE, "r")
     if lockF then
+        local content = lockF:read("*a")
         lockF:close()
-        return
+        local lockTime = tonumber(content)
+        if lockTime and (os.time() - lockTime) < 5 then
+            return  -- Still running, ignore
+        end
+        -- Stale lock, remove and continue
+        os.remove(LOCK_FILE)
     end
-    -- Create lock file
+    -- Create lock file with current timestamp
     local lf = io.open(LOCK_FILE, "w")
-    if lf then lf:write("running"); lf:close() end
+    if lf then lf:write(tostring(os.time())); lf:close() end
 
     S.currentTab = "Animations"
     refreshSource()