feat: add application config overview and inline editing

Add admin page at /admin/appconfig with a DataTable showing all
application configurations. Inline dropdowns allow editing log level,
engine level, payload capture mode, and metrics toggle directly from
the table. Changes push to agents via SSE immediately.

Also adds a config bar on the AgentHealth page (/agents/:appId) for
per-application config management with the same 4 settings.

Backend: GET /api/v1/config list endpoint, findAll() on repository,
sensible defaults for logForwardingLevel/engineLevel/payloadCaptureMode.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/Admin/AppConfigPage.module.css

@@ -0,0 +1,53 @@
+.inspectLink {
+  background: transparent;
+  border: none;
+  color: var(--text-faint);
+  opacity: 0.75;
+  cursor: pointer;
+  font-size: 13px;
+  padding: 2px 4px;
+  border-radius: var(--radius-sm);
+  line-height: 1;
+  display: inline-flex;
+}
+
+.inspectLink:hover {
+  color: var(--text-primary);
+  opacity: 1;
+}
+
+.inlineSelect {
+  padding: 3px 8px;
+  border: 1px solid var(--border-subtle);
+  border-radius: var(--radius-sm);
+  background: var(--bg-body);
+  color: var(--text-primary);
+  font-size: 11px;
+  font-family: var(--font-mono);
+  outline: none;
+  cursor: pointer;
+}
+
+.inlineSelect:focus {
+  border-color: var(--amber);
+}
+
+.inlineSelect:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
+.inlineToggle {
+  display: flex;
+  align-items: center;
+  gap: 5px;
+  font-size: 11px;
+  font-family: var(--font-mono);
+  color: var(--text-secondary);
+  cursor: pointer;
+}
+
+.inlineToggle input {
+  accent-color: var(--amber);
+  cursor: pointer;
+}