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/config.rs

@@ -53,6 +53,10 @@ pub struct Config {
     pub llm_model: String,
     pub llm_temperature: f32,
     pub session_timeout_hours: u32,
+    /// Whether to set the `Secure` flag on the session cookie. Default `true`.
+    /// Set `COOKIE_SECURE=false` only for plain-HTTP local development —
+    /// browsers refuse `Secure` cookies on non-HTTPS origins.
+    pub cookie_secure: bool,
 }
 
 impl Config {
@@ -82,6 +86,7 @@ impl Config {
             llm_model: optional_env("LLM_MODEL", ""),
             llm_temperature: optional_env_parsed("LLM_TEMPERATURE", 0.0),
             session_timeout_hours: optional_env_parsed("SESSION_TIMEOUT_HOURS", 8),
+            cookie_secure: optional_env_parsed("COOKIE_SECURE", true),
         }
     }
 }