feat: Implement directory validation and shell command quoting

- Added is_valid_directory function to validate directory paths, ensuring they do not contain control characters and are within a specified length.
- Introduced quote_shell_arg to safely quote shell arguments, preventing command injection.
- Created build_cd_command to generate a command for changing directories in a shell.
- Enhanced the LoginHandler to utilize a login rate limiter, preventing brute-force attacks by tracking failed login attempts.
- Implemented an EncodingCache to optimize encoding detection for SSH connections.
- Updated the UI to include an input field for specifying an initial directory upon login, with appropriate validation and hints.
- Added a quickbar in the terminal interface for easy access to copy and paste functionality.
- Introduced a toast notification system to provide feedback on copy actions.
- Refactored connection storage to encrypt passwords at rest, improving security.
- Updated various templates and styles to accommodate new features and improve user experience.

README.md

@@ -109,7 +109,8 @@ var opts = {
   password: 'password',
   privatekey: 'the private key text',
   passphrase: 'passphrase',
-  totp: 'totp'
+  totp: 'totp',
+  directory: '/var/www'
 };
 wssh.connect(opts);
 
@@ -169,6 +170,11 @@ Passing a command executed right after login
 http://localhost:8888/?command=pwd
 ```
 
+Passing an initial working directory (the shell runs `cd` right after login)
+```bash
+http://localhost:8888/?hostname=xx&username=yy&directory=/var/www
+```
+
 Passing a terminal type
 ```bash
 http://localhost:8888/?term=xterm-256color
@@ -181,6 +187,11 @@ Start up the app
 docker compose up -d
 ```
 
+Rebuild after changing the code
+```
+docker compose up -d --build
+```
+
 Tear down the app
 ```
 docker compose down
@@ -189,6 +200,27 @@ docker compose down
 The bundled compose file persists login and saved connection data in the
 `webssh-data` volume mounted at `/data` inside the container.
 
+Extra options can be passed without rebuilding the image via `WEBSSH_OPTS`:
+```
+WEBSSH_OPTS="--maxconn=50 --tdstream=172.18.0.1" docker compose up -d
+```
+
+Set `--tdstream` to your reverse proxy address whenever `xheaders` is on
+(the default). Without it any client can spoof `X-Forwarded-For` and claim
+someone else's address, which defeats the per-client connection limit.
+
+### Saved connections
+
+Saved SSH passwords are encrypted at rest in `connections.json` with a key
+derived from the server secret, and are never sent to the browser. Leaving
+the password field empty for a saved host tells the server to use the one it
+already holds; editing the hostname, port or username makes it a different
+destination, so the stored credential is not reused there.
+
+The server secret lives in `<data-dir>/cookie_secret` and can be overridden
+with the `WEBSSH_COOKIE_SECRET` environment variable. Losing it does not break
+the app, but saved passwords become unreadable and have to be entered again.
+
 ### Tests
 
 Requirements