Add Image Security Toolkit (tools)

Library:
- Add peek_image() to detect Stegasoo headers without decrypting

CLI:
- stegasoo tools capacity <image> - show LSB/DCT capacity
- stegasoo tools strip <image> - remove EXIF metadata
- stegasoo tools peek <image> - detect hidden data

API:
- POST /api/tools/capacity
- POST /api/tools/strip-metadata
- POST /api/tools/peek

WebUI:
- /tools page with tabbed interface (login required)
- Basic implementation - needs polish (dropzones, better results)

Architecture: Library -> CLI -> API -> WebUI pattern

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontends/web/templates/base.html

@@ -38,6 +38,9 @@
                     <li class="nav-item">
                         <a class="nav-link" href="/about"><i class="bi bi-info-circle me-1"></i> About</a>
                     </li>
+                    <li class="nav-item">
+                        <a class="nav-link" href="/tools"><i class="bi bi-tools me-1"></i> Tools</a>
+                    </li>
                     {% if auth_enabled %}
                         {% if is_authenticated %}
                         <li class="nav-item dropdown">