[feat] Adds a context-aware schema visualizer, modernizes the UI, and bugfixes

[floydtree]

Visual Refresh

• Updated CSS design system: Inter font, refined color palette (teal primary), improved spacing and typography
• Sidebar options revamped with pill toggle switches (Dark mode, Compact view, Show deprecated)
• Added global compact/wide layout toggle (persisted via localStorage)
• Moved theme toggle from top navbar into sidebar Options section

Context-Aware Visualizer (inspired by #177)

• New /visualizer route rendered as a Phoenix template within the app layout
• Accessible via "Visualizer" button on class, object, and category pages
• Scoped graph showing only relevant relationships: parent category, parent class (extends), and object-type attributes as connected nodes
• Double-click navigation between nodes (loads that entity's visualizer)
• Profile/extension filtering respected in graph data (API calls forward current selection)
• Deprecated annotations: deprecated objects/classes shown with dashed amber border, deprecated attribute edges shown as amber dashed lines, "D" badge in detail panel
• Show/hide deprecated toggle updates graph in real-time
• Cytoscape.js served locally (no CDN dependency)
• Removed old vis-network graph pages (/class/graph/, /object/graph/), templates, Schema.Graph module, and vis-network.min.js (702KB)

Bug fixes

• Profile auto-selection bug: updateProfileVisibility() no longer writes to localStorage on page load, breaking the self-reinforcing loop
• Extension/profile URL handling: Changes preserve context params (e.g., class=X) when toggling extensions/profiles on the visualizer page
• Extension-scoped entities: Visualizer correctly handles ext/class_name style scoped names, consistent with the rest of the app

[PR0CK0]

Hooray for the visualizer! Pleasure working with you @floydtree.