APP_ENV removal and secure cookie handling (#333)

Hey, made the tweaks we discussed, plus a couple related fixes :)

- Removed APP_ENV entirely. All dev-specific functionality is enabled
via `DEBUG: true` env var
- Set secure cookie handling to false by default, added to the readme to
enable if exclusively using HTTPS connection
- Fixed healthcheck potentially not working with auth enabled
- Removed APP_ENV from docker compose files and made sure app.db lines
are included in all versions.

APP_ENV in people's existing composes should get ignored entirely and
will be put on the default env, so no issues when updating.

src/frontend/src/App.tsx

@@ -490,9 +490,9 @@ function App() {
       </main>
 
       <Footer 
-        buildVersion={config?.build_version || 'dev'} 
-        releaseVersion={config?.release_version || 'dev'} 
-        appEnv={config?.app_env || 'development'}
+        buildVersion={config?.build_version} 
+        releaseVersion={config?.release_version} 
+        debug={config?.debug}
       />
       <ToastContainer toasts={toasts} />
       

src/frontend/src/components/Footer.tsx

@@ -1,10 +1,15 @@
 interface FooterProps {
   buildVersion?: string;
   releaseVersion?: string;
-  appEnv?: string;
+  debug?: boolean;
 }
 
-export const Footer = ({ buildVersion, releaseVersion, appEnv }: FooterProps) => {
+export const Footer = ({ buildVersion, releaseVersion, debug }: FooterProps) => {
+  // Determine version display - show "dev" if no version is set
+  const versionDisplay = releaseVersion && releaseVersion !== 'N/A' 
+    ? releaseVersion 
+    : 'dev';
+  
   return (
     <footer
       className="mt-8 border-t py-6"
@@ -17,8 +22,9 @@ export const Footer = ({ buildVersion, releaseVersion, appEnv }: FooterProps) =>
         <div className="min-w-0 text-left">
           <p className="text-sm opacity-80">Calibre Web Book Downloader</p>
           <p className="text-xs opacity-60 mt-1">
-            Build: {buildVersion || 'dev'} • Release: {releaseVersion || 'dev'} • Env:{' '}
-            {appEnv || 'development'}
+            Version: {versionDisplay}
+            {buildVersion && buildVersion !== 'N/A' && ` (${buildVersion})`}
+            {debug && ' • Debug Mode'}
           </p>
         </div>
         <div className="flex items-center gap-3 shrink-0">

src/frontend/src/types/index.ts

@@ -71,7 +71,6 @@ export interface Toast {
 export interface AppConfig {
   calibre_web_url: string;
   debug: boolean;
-  app_env: string;
   build_version: string;
   release_version: string;
   book_languages: Language[];