feat: inspector page, link debug enhancements, security hardening

- Add /inspector page: visual model-accurate switch chassis diagrams
  (USF5P, USL8A, US24PRO, USPPDUP, USMINI), clickable port blocks
  with color coding (green=up, amber=PoE, cyan=uplink, grey=down),
  detail panel with stats/PoE/LLDP, LLDP-based path debug side-by-side

- Link Debug: port number badges (#N), LLDP neighbor line, PoE class/max,
  collapsible host/switch panels with sessionStorage persistence

- monitor.py: collect LLDP neighbor map + PoE class/max/mode per switch
  port; PulseClient uses requests.Session() for HTTP keep-alive; add
  shlex.quote() around interface names (defense-in-depth)

- Security: suppress buttons use data-* attrs + delegated click handler
  instead of inline onclick with Jinja2 variable interpolation; remove
  | safe filter from user-controlled fields in suppressions.html;
  setDuration() takes explicit el param instead of implicit event global

- db.py: thread-local connection reuse with ping(reconnect=True) to
  avoid a new TCP handshake per query

- .gitignore: add config.json (contains credentials), __pycache__

- README: full rewrite covering architecture, all 4 pages, alert logic,
  config reference, deployment, troubleshooting, security notes

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

db.py

@@ -1,6 +1,7 @@
 """Database operations for Gandalf network monitor."""
 import json
 import logging
+import threading
 from contextlib import contextmanager
 from datetime import datetime, timedelta
 from typing import Optional
@@ -11,6 +12,7 @@ import pymysql.cursors
 logger = logging.getLogger(__name__)
 
 _config_cache = None
+_local = threading.local()
 
 
 def _config() -> dict:
@@ -23,22 +25,25 @@ def _config() -> dict:
 
 @contextmanager
 def get_conn():
+    """Yield a per-thread cached database connection, reconnecting as needed."""
     cfg = _config()
-    conn = pymysql.connect(
-        host=cfg['host'],
-        port=cfg.get('port', 3306),
-        user=cfg['user'],
-        password=cfg['password'],
-        database=cfg['name'],
-        autocommit=True,
-        cursorclass=pymysql.cursors.DictCursor,
-        connect_timeout=10,
-        charset='utf8mb4',
-    )
-    try:
-        yield conn
-    finally:
-        conn.close()
+    conn = getattr(_local, 'conn', None)
+    if conn is None:
+        conn = pymysql.connect(
+            host=cfg['host'],
+            port=cfg.get('port', 3306),
+            user=cfg['user'],
+            password=cfg['password'],
+            database=cfg['name'],
+            autocommit=True,
+            cursorclass=pymysql.cursors.DictCursor,
+            connect_timeout=10,
+            charset='utf8mb4',
+        )
+        _local.conn = conn
+    else:
+        conn.ping(reconnect=True)
+    yield conn
 
 
 # ---------------------------------------------------------------------------