fix: LLDP port label bug, suppression SQL dead code, avatar path hardening

- inspector.html: fix LLDP neighbor label in port blocks — port.lldp_table never exists; data is at port.lldp (dict with system_name/chassis_id); both port block renderers corrected
- db.py: remove dead 'target_detail IS NULL' branch in suppression check — target_detail is always stored as '' not NULL; query simplified to target_detail=''
- app.py: resolve cache_dir/cache_file/sentinel to absolute paths; guard against path escape before use
- app.py: wrap sentinel os.path.getmtime() in try/except OSError to handle TOCTOU deletion race

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

templates/inspector.html

@@ -107,10 +107,8 @@ function portBlockHtml(idx, port, swName, sfpBlock) {
   const sfpCls    = sfpBlock ? ' sfp-block' : '';
   const speedTxt  = portSpeedLabel(port);
   // LLDP neighbor: first 6 chars of hostname
-  const lldpName  = (port && port.lldp_table && port.lldp_table.length)
-                    ? escHtml((port.lldp_table[0].chassis_id_subtype === 'local'
-                        ? port.lldp_table[0].chassis_id
-                        : port.lldp_table[0].system_name || port.lldp_table[0].chassis_id || '').slice(0, 6))
+  const lldpName  = (port && port.lldp && (port.lldp.system_name || port.lldp.chassis_id))
+                    ? escHtml((port.lldp.system_name || port.lldp.chassis_id || '').slice(0, 6))
                     : '';
   const lldpHtml  = lldpName ? `<span class="port-lldp">${lldpName}</span>` : '';
   const speedHtml = speedTxt ? `<span class="port-speed">${speedTxt}</span>` : '';
@@ -162,10 +160,8 @@ function renderChassis(swName, sw) {
         const state  = portBlockState(port);
         const title  = port ? escHtml(port.name) : `Port ${idx}`;
         const speedTxt  = portSpeedLabel(port);
-        const lldpName  = (port && port.lldp_table && port.lldp_table.length)
-                          ? escHtml((port.lldp_table[0].chassis_id_subtype === 'local'
-                              ? port.lldp_table[0].chassis_id
-                              : port.lldp_table[0].system_name || port.lldp_table[0].chassis_id || '').slice(0, 6))
+        const lldpName  = (port && port.lldp && (port.lldp.system_name || port.lldp.chassis_id))
+                          ? escHtml((port.lldp.system_name || port.lldp.chassis_id || '').slice(0, 6))
                           : '';
         const speedHtml = speedTxt ? `<span class="port-speed">${speedTxt}</span>` : '';
         const lldpHtml  = lldpName ? `<span class="port-lldp">${lldpName}</span>` : '';