feat(ui/ux): comprehensive UX overhaul and documentation sync

[snehmatic]

Closes #98

This PR introduces a comprehensive UI and UX overhaul across the entire Mindloop web application, followed by a documentation sync to reflect all new visual and structural changes.

Key Changes

• Comprehensive Visual Refresh: Implemented a new, premium "Teal and Action Orange" color palette. Introduced a refined typography system, layered shadows (shadow-glow), and modern pill-shaped UI components.
• Enhanced Dark Mode: Upgraded dark mode with a deep, OLED-like Slate-Teal background (#050b14) for improved contrast and low-light comfort.
• Navigation & Layout Updates: Reorganized the top navigation bar, adding a unified "Write" dropdown that consolidates Journal and Notes access. Added animated interactions for nav links.
• Component Redesign: Upgraded UI controls across the board, introducing segmented controls, toggle switches, and cleaner card layouts (especially visible in Settings and Tasks).
• View Simplification: Significantly refactored and streamlined individual entity views (journal_view.html, note_view.html, habit_view.html) for a snappier, less cluttered experience.
• New Features Integrated: Fully integrated UI for Tasks, Sub-tasks, and the new "Void" feature.
• Documentation Sync: Updated docs/web_ui.md, docs/ARCHITECTURE_UI.md, and docs/FEATURES.md with new details and fresh screenshots to match the new interface.