feat(db): backfill, DB-backed web scans, firewall snapshot view (R001/S001/F001)

- R001: app/db/backfill.py imports git-history blocklist -> ledger, firewall
  snapshots, and per-source requests.csv (idempotent; ran live migrating 705
  historical blocklist entries).
- S001: web_scan.latest_scans() now merges SQLite 'scans' records so the
  dashboard surfaces CLI/restart scans (_db_scans).
- F001: /api/firewall/snapshots + 'Snapshot history' panel; added
  recent_firewall_snapshots() query with entry counts.

app/templates/firewall.html

@@ -23,6 +23,11 @@ endblock %} {% block content %}
   <div class="panel-head"><h2>Firewall rules</h2></div>
   <div id="firewall-rules"></div>
 </div>
+
+<div class="panel">
+  <div class="panel-head"><h2>Snapshot history (SQLite)</h2></div>
+  <div id="fw-snapshots"></div>
+</div>
 {% endblock %} {% block scripts %}
 <script>
   async function loadState() {
@@ -35,6 +40,45 @@ endblock %} {% block content %}
     }
   }
 
+  async function loadSnapshots() {
+    const box = document.getElementById("fw-snapshots");
+    try {
+      const d = await api("/api/firewall/snapshots?limit=10");
+      const snaps = d.snapshots || [];
+      if (!snaps.length) {
+        box.innerHTML =
+          '<p class="muted">No SQLite snapshots yet — they are recorded on each <code>--update-firewall</code> run.</p>';
+        return;
+      }
+      box.innerHTML = "";
+      const rows = snaps.map((s) =>
+        el(
+          "tr",
+          el("td", { class: "mono", text: `#${s.id}` }),
+          el("td", { text: fmtTime(s.captured_at) }),
+          el("td", { text: s.kind }),
+          el("td", { text: s.trigger }),
+          el("td", { class: "num", text: s.addr_entries }),
+          el("td", { class: "num", text: s.rule_entries }),
+        ),
+      );
+      box.append(
+        el(
+          "table",
+          { class: "table" },
+          el(
+            "thead",
+            el("tr", {}, el("th", { text: "ID" }), el("th", { text: "Captured" }), el("th", { text: "Kind" }), el("th", { text: "Trigger" }), el("th", { text: "Addr" }), el("th", { text: "Rules" })),
+          ),
+          el("tbody", {}, ...rows),
+        ),
+      );
+    } catch (e) {
+      box.innerHTML=
+        '<p class="muted">Snapshot history unavailable (SQLite).</p>';
+    }
+  }
+
   function renderAddressLists(addr) {
     const box = document.getElementById("address-lists");
     box.innerHTML = "";
@@ -172,5 +216,6 @@ endblock %} {% block content %}
     .getElementById("apply-btn")
     .addEventListener("click", () => sync(false));
   loadState();
+  loadSnapshots();
 </script>
 {% endblock %}