feat: add DB Explorer for read-only SQLite inspection

Adds /db-explorer page and JSON API to browse all 15 SQLite databases
in data/. Sidebar lists databases with sizes, clicking one renders all
tables as scrollable data tables with row truncation at 200.

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

static/css/mission-control.css

@@ -2463,3 +2463,33 @@
     font-size: 0.7rem;
   }
 }
+
+/* ═══════════════════════════════════════════════════════════════
+   DB Explorer
+   ═══════════════════════════════════════════════════════════════ */
+
+.db-explorer-container { max-width: 1400px; margin: 0 auto; padding: 0 1rem; }
+.db-explorer-header { margin-bottom: 0.5rem; }
+.db-explorer-title { font-size: 1.4rem; font-weight: 700; color: var(--text-bright); letter-spacing: 0.05em; }
+.db-explorer-subtitle { font-size: 0.75rem; color: var(--text-dim); }
+
+.db-list { display: flex; flex-direction: column; gap: 2px; }
+.db-list-item {
+  display: flex; justify-content: space-between; align-items: center;
+  padding: 0.45rem 0.6rem; border-radius: 4px;
+  color: var(--text); text-decoration: none;
+  transition: background 0.15s;
+}
+.db-list-item:hover { background: var(--bg-card); color: var(--text-bright); }
+.db-list-item.active { background: var(--purple); color: var(--text-bright); }
+.db-name { font-size: 0.8rem; font-weight: 600; }
+.db-size { font-size: 0.7rem; color: var(--text-dim); }
+.db-list-item.active .db-size { color: var(--text-bright); opacity: 0.7; }
+
+.db-table-wrap { max-height: 500px; overflow: auto; }
+.db-table { font-size: 0.75rem; }
+.db-table th { position: sticky; top: 0; background: var(--bg-panel); color: var(--green); font-weight: 600; white-space: nowrap; z-index: 1; }
+.db-table td { vertical-align: top; }
+.db-cell { max-width: 300px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+.db-cell:hover { white-space: normal; word-break: break-all; }
+.db-truncated { font-size: 0.7rem; color: var(--amber); padding: 0.3rem 0; }