[style](trx-frontend-http): align login button width with passphrase field

Add box-sizing: border-box to both the passphrase input and login button
to ensure padding is included in width calculations. This makes them
exactly the same width visually.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -33,8 +33,8 @@
         <div style="color: var(--text-muted);">Enter passphrase to continue</div>
       </div>
       <form id="auth-form" style="margin: 1.5rem 0;">
-        <input type="password" id="auth-passphrase" placeholder="Passphrase" autocomplete="off" style="width: 100%; padding: 0.5rem; margin-bottom: 1rem; border: 1px solid var(--border); border-radius: 0.25rem; background: var(--bg-secondary); color: var(--text); font-size: 1rem;" />
-        <button type="submit" style="width: 100%; padding: 0.5rem; background: var(--accent-green); color: var(--bg-primary); border: none; border-radius: 0.25rem; font-weight: 600; cursor: pointer; font-size: 1rem;">Login</button>
+        <input type="password" id="auth-passphrase" placeholder="Passphrase" autocomplete="off" style="width: 100%; padding: 0.5rem; margin-bottom: 1rem; border: 1px solid var(--border); border-radius: 0.25rem; background: var(--bg-secondary); color: var(--text); font-size: 1rem; box-sizing: border-box;" />
+        <button type="submit" style="width: 100%; padding: 0.5rem; background: var(--accent-green); color: var(--bg-primary); border: none; border-radius: 0.25rem; font-weight: 600; cursor: pointer; font-size: 1rem; box-sizing: border-box;">Login</button>
       </form>
       <div id="auth-error" style="color: #ff6b6b; font-size: 0.9rem; margin-top: 1rem; display: none;"></div>
       <div id="auth-role" style="margin-top: 1rem; color: var(--text-muted); font-size: 0.85rem; display: none;"></div>