feat(admin): show the resolved data directory in Settings

Prompted by not being able to tell where a locally-run instance's data dir
actually was without inspecting the running process (ps/lsof). Adds
data_dir to /api/setup/version's response, resolved to an absolute path so
it's unambiguous regardless of whether --data-dir/DATA_DIR was relative or
left at the default.

Shown as a read-only line at the top of the Settings tab, not the always-
visible footer — the footer is prime real estate seen on every tab/every
page load, and this is a rarely-needed piece of diagnostic info that
belongs alongside the rest of System Settings instead.

Also filled in a test-helper gap: the pkg/service/handlers package's
internal test router (main_test.go) never registered /setup/version at
all, unlike the real production router — added it so the new test (and any
future one exercising this endpoint) can actually run.

Unrelated to #419, but found while verifying that work against a running
instance.

pkg/service/handlers/handlers_setup.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"net/http"
 	"os"
+	"path/filepath"
 	"sort"
 	"strconv"
 	"strings"
@@ -1357,6 +1358,19 @@ func (s *Server) HandleGetVersionInfo(w http.ResponseWriter, _ *http.Request) {
 	repoURL := s.RepoURL
 	s.mu.RUnlock()
 
+	var dataDir string
+
+	if s.ds != nil && s.ds.DataDir != "" {
+		// Resolve to absolute: the default ("data") and any relative
+		// --data-dir/DATA_DIR value are otherwise ambiguous without knowing
+		// the process's working directory at startup.
+		if abs, err := filepath.Abs(s.ds.DataDir); err == nil {
+			dataDir = abs
+		} else {
+			dataDir = s.ds.DataDir
+		}
+	}
+
 	w.Header().Set("Content-Type", "application/json")
 
 	var (
@@ -1381,6 +1395,7 @@ func (s *Server) HandleGetVersionInfo(w http.ResponseWriter, _ *http.Request) {
 		"repo_url":    repoURL,
 		"release_url": releaseURL,
 		"commit_url":  commitURL,
+		"data_dir":    dataDir,
 	}); err != nil {
 		http.Error(w, "Failed to encode response", http.StatusInternalServerError)
 		return

pkg/service/handlers/handlers_setup_test.go

@@ -443,6 +443,46 @@ func TestAdminAreaAuthRoundTrip(t *testing.T) {
 	}
 }
 
+// TestHandleGetVersionInfo_IncludesAbsoluteDataDir verifies /api/setup/version
+// reports the actual data directory in use, resolved to an absolute path —
+// added so operators running the service locally (not in Docker, where the
+// path is obvious from the bind mount) can find it without having to
+// inspect the running process. See NEXT.md/#419 session notes.
+func TestHandleGetVersionInfo_IncludesAbsoluteDataDir(t *testing.T) {
+	tempDir, err := os.MkdirTemp("", "version-info-datadir-test")
+	if err != nil {
+		t.Fatalf("Failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tempDir)
+
+	ds := datastore.NewDataStore(tempDir)
+	_ = ds.Initialize()
+
+	r, _ := setupRouter("http://127.0.0.1:8000", ds)
+	ts := httptest.NewServer(r)
+	defer ts.Close()
+
+	res, err := http.Get(ts.URL + "/setup/version")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer res.Body.Close()
+
+	var got map[string]string
+	if err := json.NewDecoder(res.Body).Decode(&got); err != nil {
+		t.Fatalf("Failed to decode response: %v", err)
+	}
+
+	wantAbs, err := filepath.Abs(tempDir)
+	if err != nil {
+		t.Fatalf("Failed to resolve expected absolute path: %v", err)
+	}
+
+	if got["data_dir"] != wantAbs {
+		t.Errorf("Expected data_dir %q, got %q", wantAbs, got["data_dir"])
+	}
+}
+
 func TestMigrationAndCA(t *testing.T) {
 	tempDir, err := os.MkdirTemp("", "handlers-test")
 	if err != nil {

pkg/service/handlers/main_test.go

@@ -131,6 +131,7 @@ func setupRouter(targetURL string, ds *datastore.DataStore) (*chi.Mux, *Server)
 		r.Delete("/devices/{deviceId}", server.HandleRemoveDevice)
 		r.Get("/settings", server.HandleGetSettings)
 		r.Post("/settings", server.HandleUpdateSettings)
+		r.Get("/version", server.HandleGetVersionInfo)
 		r.Get("/logging-settings", server.HandleGetLoggingSettings)
 		r.Post("/logging-settings", server.HandleUpdateLoggingSettings)
 		r.Post("/ensure-remote-services/{deviceId}", server.HandleEnsureRemoteServices)

pkg/service/handlers/web/index.html

@@ -171,6 +171,9 @@
     <!-- Tab 1: Settings -->
     <div id="tab-settings" class="tab-content">
         <h2>System Settings</h2>
+        <p style="font-size: 0.85em; color: #666; margin: -8px 0 20px 0;">
+            Data directory: <code id="settings-data-dir">-</code>
+        </p>
         <div style="margin-bottom: 20px">
             <strong>Service URLs</strong>
             <p style="font-size: 0.9em; color: #555; margin: 6px 0 12px 0">

pkg/service/handlers/web/js/script.js

@@ -891,6 +891,11 @@ async function fetchVersion() {
             }
             info.innerHTML = `AfterTouch ${versionStr} (${commitStr}) • ${data.date}`;
         }
+
+        const dataDirEl = document.getElementById("settings-data-dir");
+        if (dataDirEl && data.data_dir) {
+            dataDirEl.textContent = data.data_dir;
+        }
     } catch (error) {
         console.error("Failed to fetch version info", error);
     }