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>

db.py

@@ -365,7 +365,7 @@ def is_suppressed(target_type: str, target_name: str, target_detail: str = '') -
                 """SELECT id FROM suppression_rules
                    WHERE active=TRUE AND (expires_at IS NULL OR expires_at > NOW())
                    AND target_type=%s AND target_name=%s
-                   AND (target_detail IS NULL OR target_detail='') LIMIT 1""",
+                   AND target_detail='' LIMIT 1""",
                 (target_type, target_name),
             )
             if cur.fetchone():