feat: add game page frontend with grid, word list, timer, and dual input

Recreates base.html and main.html templates (lost during reset).
Adds game.html with setup UI (category picker, board size slider),
interactive grid table, word list sidebar, text input, click-to-select,
timer, and completion banner. Adds game.js for all frontend logic.
Extends theme.css with game grid and form control styles using the
indigo/coral palette.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/main.html

@@ -0,0 +1,14 @@
+{% extends "base.html" %}
+
+{% block title %}Word Search — Home{% end %}
+
+{% block content %}
+<div class="text-center py-5">
+    <h1 class="display-4 fw-bold mb-3">Word Search</h1>
+    <p class="lead mb-4">
+        Find hidden words in a grid of letters. Words can appear horizontally,
+        vertically, or diagonally. How fast can you find them all?
+    </p>
+    <a href="/game" class="btn btn-accent btn-lg px-5">Start Game</a>
+</div>
+{% end %}