Feat: Implement basic web authentication and UI

This commit introduces the foundation for web-based authentication and
user interface. It includes:

- **Session Management**: Securely handling user sessions using
  cryptographically generated tokens, cookies with appropriate security
  flags, and server-side storage.
- **Login/Logout Functionality**: Endpoints for users to log in with
  their credentials and log out, clearing their session.
- **User Interface**: Basic templates for the login page, a list of
  cases, and a detailed view of a single case, allowing users to
  navigate and view their data.
- **Authorization**: An `AuthenticatedWebUser` extractor to ensure only
  logged-in users can access protected web routes.
- **Configuration**: Added a `cookie_secure` option to the configuration
  to control the `Secure` flag on session cookies, useful for local
  development.
- **Dependencies**: Added necessary dependencies for password hashing,
  time handling, and TOML file manipulation.
- **Helper Binary**: Included a `hash-password` binary to simplify
  generating bcrypt hashes for user passwords.

server/src/bin/hash-password.rs

@@ -0,0 +1,16 @@
+//! Generate a bcrypt hash for a plaintext password.
+//! Use when adding or rotating a `web_password` entry in `users.toml`.
+//!
+//! Dev:     `cargo run --quiet --bin hash-password -- 'my-password'`
+//! Release: `./target/release/hash-password 'my-password'`
+
+fn main() {
+    let password = std::env::args().nth(1).unwrap_or_else(|| {
+        eprintln!("Usage: hash-password '<password>'");
+        std::process::exit(2);
+    });
+
+    let hash = bcrypt::hash(&password, bcrypt::DEFAULT_COST)
+        .expect("bcrypt hashing failed");
+    println!("{hash}");
+}