Add network monitoring, dashboard, and Home Assistant MQTT publishing

Keep /alive unchanged and serve a dashboard at / with status cards,
latency graphs, an event timeline, and a Wi-Fi section.

Background monitors on configurable intervals: TCP reachability,
DNS resolution, public IP change detection, host reboot detection,
Wi-Fi link quality, and Wi-Fi scan of networks in range via iw.
The Wi-Fi interface is selected with WIFI_INTERFACE; the page lists
visible interfaces and reports when none is available. Scan results
stay in memory, other metrics go to SQLite on a mounted volume.

Optional MQTT publishing with Home Assistant discovery groups all
sensors under one device per host.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TdvJYoY8kc8bmBck89U2i6

storage.py

@@ -0,0 +1,106 @@
+import os
+import sqlite3
+import time
+from contextlib import closing
+
+SCHEMA = """
+CREATE TABLE IF NOT EXISTS samples (
+    ts REAL NOT NULL,
+    metric TEXT NOT NULL,
+    value REAL
+);
+CREATE INDEX IF NOT EXISTS samples_metric_ts ON samples(metric, ts);
+CREATE TABLE IF NOT EXISTS events (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    ts REAL NOT NULL,
+    kind TEXT NOT NULL,
+    message TEXT NOT NULL
+);
+CREATE INDEX IF NOT EXISTS events_ts ON events(ts);
+CREATE TABLE IF NOT EXISTS kv (
+    key TEXT PRIMARY KEY,
+    value TEXT
+);
+"""
+
+
+def _like_prefix(prefix):
+    escaped = prefix.replace("\\", "\\\\").replace("%", "\\%").replace("_", "\\_")
+    return escaped + "%"
+
+
+class Storage:
+    def __init__(self, path):
+        directory = os.path.dirname(path)
+        if directory:
+            os.makedirs(directory, exist_ok=True)
+        self.path = path
+        with closing(self._connect()) as conn:
+            conn.executescript(SCHEMA)
+
+    def _connect(self):
+        conn = sqlite3.connect(self.path, timeout=10)
+        conn.execute("PRAGMA journal_mode=WAL")
+        return conn
+
+    def add_samples(self, pairs, ts=None):
+        ts = ts or time.time()
+        with closing(self._connect()) as conn, conn:
+            conn.executemany(
+                "INSERT INTO samples (ts, metric, value) VALUES (?, ?, ?)",
+                [(ts, metric, value) for metric, value in pairs],
+            )
+
+    def add_sample(self, metric, value, ts=None):
+        self.add_samples([(metric, value)], ts)
+
+    def add_event(self, kind, message, ts=None):
+        with closing(self._connect()) as conn, conn:
+            conn.execute(
+                "INSERT INTO events (ts, kind, message) VALUES (?, ?, ?)",
+                (ts or time.time(), kind, message),
+            )
+
+    def events(self, limit=200):
+        with closing(self._connect()) as conn:
+            rows = conn.execute(
+                "SELECT ts, kind, message FROM events ORDER BY ts DESC, id DESC LIMIT ?",
+                (limit,),
+            ).fetchall()
+        return [{"ts": ts, "kind": kind, "message": message} for ts, kind, message in rows]
+
+    def samples_by_prefix(self, prefix, since, bucket):
+        bucket = max(1, int(bucket))
+        with closing(self._connect()) as conn:
+            rows = conn.execute(
+                """
+                SELECT metric, CAST(ts / ? AS INTEGER) * ? AS bucket, AVG(value)
+                FROM samples
+                WHERE metric LIKE ? ESCAPE '\\' AND ts >= ?
+                GROUP BY metric, bucket
+                ORDER BY metric, bucket
+                """,
+                (bucket, bucket, _like_prefix(prefix), since),
+            ).fetchall()
+        series = {}
+        for metric, ts, value in rows:
+            series.setdefault(metric, []).append([ts, value])
+        return series
+
+    def get(self, key):
+        with closing(self._connect()) as conn:
+            row = conn.execute("SELECT value FROM kv WHERE key = ?", (key,)).fetchone()
+        return row[0] if row else None
+
+    def set(self, key, value):
+        with closing(self._connect()) as conn, conn:
+            conn.execute(
+                "INSERT INTO kv (key, value) VALUES (?, ?) "
+                "ON CONFLICT(key) DO UPDATE SET value = excluded.value",
+                (key, value),
+            )
+
+    def prune_samples(self, days):
+        cutoff = time.time() - days * 86400
+        with closing(self._connect()) as conn, conn:
+            conn.execute("DELETE FROM samples WHERE ts < ?", (cutoff,))