feat: refactor agent manager, media library, and player UX

- Split admin users page into player/tier-1/tier-2 tabs with affiliation labels and context-specific create dialogs

- Add media library with uploaded_files migration, list/delete unused files API, and admin nav route

- Enforce player username format (alphanumeric 3-32) on frontend and backend via shared package

- Improve admin dialog/panel styling; refine player parlay and match bet card kickoff display

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/admin/src/views/agent/Players.vue

@@ -747,7 +747,8 @@ function statusTagType(s: string) {
       />
       <el-form label-width="100px" class="create-form">
         <el-form-item :label="t('user.col.username')" required>
-          <el-input v-model="createForm.username" :placeholder="t('agent_portal.username_ph')" />
+          <el-input v-model="createForm.username" :placeholder="t('user.ph.username_player')" />
+          <div class="field-hint">{{ t('user.hint.username_player') }}</div>
         </el-form-item>
         <el-form-item :label="t('user.field.password')" required>
           <el-input v-model="createForm.password" type="text" autocomplete="off" />
@@ -783,7 +784,8 @@ function statusTagType(s: string) {
           <el-tag :type="statusTagType(editForm.status)" size="small">{{ statusLabel(editForm.status) }}</el-tag>
         </div>
         <el-form-item :label="t('user.col.username')">
-          <el-input v-model="editForm.username" :placeholder="t('user.ph.username_unique')" />
+          <el-input v-model="editForm.username" :placeholder="t('user.ph.username_player')" />
+          <div class="field-hint">{{ t('user.hint.username_player') }}</div>
         </el-form-item>
         <div class="password-mgmt-block">
           <div class="block-title">{{ t('user.section.password_mgmt') }}</div>