deps: bump tui-big-text from 0.7.3 to 0.8.1 and add UI screenshots (#88)

* deps: bump tui-big-text from 0.7.3 to 0.8.1

Bumps [tui-big-text](https://github.com/joshka/tui-widgets) from 0.7.3 to 0.8.1.
- [Release notes](https://github.com/joshka/tui-widgets/releases)
- [Changelog](https://github.com/joshka/tui-widgets/blob/main/CHANGELOG.md)
- [Commits](ratatui/tui-widgets@tui-big-text-v0.7.3...tui-big-text-v0.8.1)

---
updated-dependencies:
- dependency-name: tui-big-text
  dependency-version: 0.8.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

* deps: bump ratatui from 0.29 to 0.30

Required for compatibility with tui-big-text 0.8.1 which uses ratatui-core 0.1.0

* docs: add UI screenshots to README

---------

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: bug-ops

README.md

@@ -10,6 +10,8 @@
 
 Stop learning commands in isolation. Train real development workflows with FSRS-powered spaced repetition (20-30% faster mastery), daily quests, XP progression, and anti-farming mechanics that ensure genuine skill development.
 
+<img src="assets/main-menu.png" width="600" alt="Main Menu">
+
 > [!IMPORTANT]
 > **100% Offline & Privacy-First** — No internet required, no telemetry, no cloud sync. All data stays on your machine in `~/.config/helix-trainer/`
 
@@ -24,8 +26,12 @@ Stop learning commands in isolation. Train real development workflows with FSRS-
 - **Anti-Farming Protection** — Session penalties prevent XP exploitation
 - **Profile & Statistics** — Track your progress, view mastery levels, and see performance analytics
 
+<img src="assets/profile.png" width="600" alt="Player Profile">
+
 ### Mini-Games Mode
 
+<img src="assets/arcade-mode.png" width="600" alt="Arcade Mode">
+
 - **Arcade Training** — 60-second timed sessions with automatic scenario progression
 - **Streak Multiplier** — Build combos up to 5x for consecutive completions
 - **Lives System** — Start with 3 lives, earn bonus lives at score milestones
@@ -191,7 +197,7 @@ All commands powered by `helix-core` v25.07.1 for 100% accuracy.
 
 Most Helix/Vim tutorials:
 
-- Teach `dd` (delete line) in isolation ❌
+- Teach `xd` (delete line) in isolation ❌
 - Show `w` (next word) on synthetic text ❌
 - Stop at "congratulations, you know the basics!" ❌