fix: improve UI and login functionality

* update UI components and layout
* fix login form functionality
* pin Docker base image to python:3.11-slim-bookworm

deployment/Dockerfile

@@ -1,6 +1,6 @@
 # Multi-stage Dockerfile for WebSSH - Optimized for small image size
 # Stage 1: Builder - compiles Python packages with build dependencies
-FROM python:3.11-slim AS builder
+FROM python:3.11-slim-bookworm AS builder
 
 # Install build dependencies needed for compiling cryptography/pynacl on arm/v7
 RUN apt-get update && apt-get install -y --no-install-recommends \
@@ -95,7 +95,7 @@ RUN set -eux; \
     if command -v strip >/dev/null 2>&1; then strip --strip-unneeded /tmp/caddy_bin_dir/caddy || true; fi
 
 # Stage 2: Final - minimal runtime image
-FROM python:3.11-slim
+FROM python:3.11-slim-bookworm
 
 # Install only runtime dependencies (no build tools)
 RUN apt-get update && apt-get install -y --no-install-recommends \