Remove quota feature (incompatible with ZFS-backed LXC)

Linux setquota/repquota require quota support on the underlying
filesystem. The target deployment is a Proxmox LXC on ZFS storage where
this is not available inside the container.

Removed: /api/quota endpoint, _quota_supported, _quota_usage,
_find_quota_fs, quotas.js, quota modal, dashboard quota table,
Quota button from share rows.

PLANNING.md updated: notes quota as out of scope with reason.

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

templates/index.html

@@ -31,23 +31,6 @@
     </div>
 </div>
 
-<!-- Quota modal -->
-<div class="modal fade" id="quotaModal" tabindex="-1">
-    <div class="modal-dialog">
-        <div class="modal-content">
-            <div class="modal-header">
-                <h5 class="modal-title" id="quotaModalTitle">Set Quota</h5>
-                <button type="button" class="btn-close btn-close-white" data-bs-dismiss="modal"></button>
-            </div>
-            <div class="modal-body" id="quotaModalBody"></div>
-            <div class="modal-footer">
-                <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Cancel</button>
-                <button type="button" class="btn btn-primary" onclick="submitQuota()">Apply</button>
-            </div>
-        </div>
-    </div>
-</div>
-
 <!-- Edit Share modal -->
 <div class="modal fade" id="editModal" tabindex="-1">
     <div class="modal-dialog">
@@ -163,15 +146,6 @@
                 </table>
             </div>
 
-            <div class="fw-semibold mb-2">Quota Usage</div>
-            <div class="table-responsive">
-                <table class="table table-striped mb-0">
-                    <thead><tr><th>User</th><th>Used</th><th>Soft limit</th><th style="min-width:200px">Usage</th></tr></thead>
-                    <tbody id="dashQuotasBody">
-                        <tr><td colspan="4" style="color:var(--muted)">Loading…</td></tr>
-                    </tbody>
-                </table>
-            </div>
         </div>
 
         <!-- SMB -->
@@ -245,7 +219,6 @@
 <script src="{{ url_for('static', filename='js/utils.js') }}"></script>
 <script src="{{ url_for('static', filename='js/dashboard.js') }}"></script>
 <script src="{{ url_for('static', filename='js/shares.js') }}"></script>
-<script src="{{ url_for('static', filename='js/quotas.js') }}"></script>
 <script src="{{ url_for('static', filename='js/users.js') }}"></script>
 <script src="{{ url_for('static', filename='js/main.js') }}"></script>