fix(i18n): localize statistics page and troops Hero label [#197]

On a fresh install several strings were still hardcoded in English
(reported on the live server, RO locale):

- statistiken.php: the page <title>, the <h1> and the tab bar
  (Player / Alliances / Villages / Heroes / General) were literal English.
- Templates/Ranking/ranksearch.tpl: the "back | forward" pagination links.
- Templates/troops.tpl: the "Hero" troop-row label.

Wire them to language constants. Reuse existing ones
(STATISTICS, PLAYER, PLAYERS, VILLAGES, BACK, FORWARD, U0) and add three
new constants (ALLIANCES, HEROES, GENERAL) to en/fr/ro. WW is kept as-is
(universal acronym).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Templates/troops.tpl

@@ -115,7 +115,7 @@ if (!empty($troops['hero'])) {
         </td>
 
         <td class="un">
-            Hero
+            ' . U0 . '
         </td>
     </tr>';