Add local login, agent extra log paths, IPv4/IPv6 metrics; remediate security audit findings

This is a large squashed commit covering two batches of prior uncommitted
work plus a full security-audit remediation pass, kept together because
go.mod/go.sum and several shared files (main.go, handler.go) were touched
by both and splitting risked non-building intermediate commits.

Features (built earlier, previously uncommitted):
- Local username/password login for single-tenant deployments with no
  SSO configured (api/localauth, alerting/internal/sessioncheck,
  sentryctl users, web/src/routes/login, metadata migrations 0040/0041).
- Remotely-editable additional log file paths for agents, on top of
  their existing primary source (api/agents, agent/sentry-agent
  extra-file-path diffing, web agent config UI).
- IPv4/IPv6 addresses reported alongside other host system metrics.

Security audit remediation (this pass, all live-verified in production):
- Critical: block ClickHouse SSRF table functions (url/remote/file/s3/...)
  in the raw-SQL query escape hatch.
- High: deny sensitive paths and require Admin to add agent
  extra_file_paths (Editor could previously point an agent at /etc/shadow
  or an SSH key); alerting webhook targets now validate against
  internal/metadata/loopback addresses, both at creation and send time;
  alerting's session middleware now enforces an Editor+ floor on
  mutating requests instead of "any authenticated session"; bumped
  goxmldsig to close a SAML signature-verification bypass (GO-2026-4753).
- Medium: per-IP login rate limiting; security response headers
  (HSTS/CSP/nosniff/X-Frame-Options/Referrer-Policy/Permissions-Policy)
  on web/nginx.conf; a DevCredentialWarnings check in every Go service's
  config loader, logging loudly at startup if a deployment is still on
  docker-compose.yml's literal dev-only credentials; dependency bumps
  (golang.org/x/text, grpc, x/net, quick-xml, h2) across every affected
  Go module and both Rust crates, including a previously-uncovered x/net
  vulnerability in deploy/operator; a new security-scan.yml CI workflow
  running cargo-deny/govulncheck/npm-audit, mirroring the existing
  license-compliance.yml matrix shape.
- Low: removed sentryctl's plaintext --password flag (shell
  history/`ps` exposure) in favor of stdin and a --password-stdin flag
  for reset-password's optional specific-password path; a dummy bcrypt
  comparison closes a login response-time username-enumeration
  side-channel.

alerting/internal/httpapi/handler.go

@@ -151,6 +151,10 @@ func (h *Handler) handleCreateTarget(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "webhook_url must not be empty")
 		return
 	}
+	if err := notifystore.ValidateWebhookURL(target.WebhookURL); err != nil {
+		writeError(w, http.StatusBadRequest, "webhook_url: "+err.Error())
+		return
+	}
 	if err := h.targets.Create(r.Context(), &target); err != nil {
 		h.logger.Error("creating notification target", "error", err)
 		writeError(w, http.StatusInternalServerError, "creating notification target failed")

alerting/internal/httpapi/handler_test.go

@@ -231,12 +231,29 @@ func TestCreateTargetRejectsInvalidKind(t *testing.T) {
 
 func TestCreateSlackTarget(t *testing.T) {
 	mux := newTestMux(newFakeRuleStore(), newFakeTargetStore(), &fakeDeliveryReader{})
-	rec := doRequest(t, mux, http.MethodPost, "/targets", `{"name": "oncall", "kind": "slack", "webhook_url": "https://hooks.slack.com/services/x"}`)
+	// A literal public IP, not a real hostname like hooks.slack.com --
+	// ValidateWebhookURL (see notifystore/ssrf.go) now resolves the
+	// target host and rejects internal/metadata addresses, so this test
+	// stays deterministic without depending on live DNS; ssrf_test.go
+	// covers the validation logic itself in depth.
+	rec := doRequest(t, mux, http.MethodPost, "/targets", `{"name": "oncall", "kind": "slack", "webhook_url": "https://8.8.8.8/services/x"}`)
 	if rec.Code != http.StatusCreated {
 		t.Fatalf("status = %d, want 201; body=%s", rec.Code, rec.Body.String())
 	}
 }
 
+// TestCreateTargetRejectsSSRFWebhookURL is the regression test for the
+// security-audit finding that target creation performed no URL
+// validation at all -- any authenticated user could point a webhook at
+// an internal or cloud-metadata address.
+func TestCreateTargetRejectsSSRFWebhookURL(t *testing.T) {
+	mux := newTestMux(newFakeRuleStore(), newFakeTargetStore(), &fakeDeliveryReader{})
+	rec := doRequest(t, mux, http.MethodPost, "/targets", `{"name": "x", "kind": "webhook", "webhook_url": "http://169.254.169.254/latest/meta-data/"}`)
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want 400; body=%s", rec.Code, rec.Body.String())
+	}
+}
+
 func TestListDeliveriesForRule(t *testing.T) {
 	deliveries := &fakeDeliveryReader{entries: []rulestore.DeliveryLogEntry{
 		{ID: 1, RuleID: "rule-1", EventType: "firing", Status: "sent"},