Drop custom auth dialog; rely on browser Basic Auth handling

Remove ImportDialog and all manual credential management. The browser
handles 401 challenges natively for same-origin fetch requests — it
shows its own credential prompt, retries, and caches the result for
the session. No JS-level auth code is needed.

- api.js: remove authHeader() and all credentials parameters
- store.js: remove credentials field
- ImportDialog.js: deleted
- AppShell.js: remove showImport/openImport/onMounted dialog machinery;
  pass importOnLoad through to PaneCP
- PaneCP.js: inline doImport() (was in ImportDialog); auto-triggers on
  mount when importOnLoad is true; shows inline import error on failure
- StatusPoller.js: remove credentials arg from fetchStatus()
- style.css: remove .se-import-dialog and .se-overlay blocks

static/components/AppShell.js

@@ -1,8 +1,7 @@
-import { h, ref, computed, onMounted, watch } from 'vue';
+import { h, ref, computed, watch } from 'vue';
 import { PaneCP } from './PaneCP.js';
 import { PaneFO } from './PaneFO.js';
 import { PaneSubObjects } from './PaneSubObjects.js';
-import { ImportDialog } from './ImportDialog.js';
 import { getKindGroups, KIND_LABEL } from '../subobject-kinds.js';
 
 const FIXED_PANES = [
@@ -14,7 +13,6 @@ export const AppShell = {
     props: ['store', 'importOnLoad'],
     setup(props) {
         const activePane = ref('cp');
-        const showImport = ref(false);
 
         function focusedNode() {
             const fp = props.store.focusPath;
@@ -35,14 +33,6 @@ export const AppShell = {
             if (!ps.some(p => p.id === activePane.value)) activePane.value = 'fo';
         });
 
-        function openImport() {
-            if (!props.store.isDirty) showImport.value = true;
-        }
-
-        onMounted(() => {
-            if (props.importOnLoad && !props.store.isDirty) showImport.value = true;
-        });
-
         return () => {
             const store = props.store;
             const ap = activePane.value;
@@ -54,7 +44,11 @@ export const AppShell = {
             return h('div', { class: 'se-shell' }, [
                 h('div', { class: 'se-pane-area' }, [
                     h('div', { class: ['se-pane', ap === 'cp' ? 'active' : null] },
-                        h(PaneCP, { store, onImportClick: openImport, onFocusFO: () => { activePane.value = 'fo'; } })),
+                        h(PaneCP, {
+                            store,
+                            importOnLoad: props.importOnLoad,
+                            onFocusFO: () => { activePane.value = 'fo'; },
+                        })),
                     h('div', { class: ['se-pane', ap === 'fo' ? 'active' : null] },
                         h(PaneFO, { store })),
                     ...subPaneNodes,
@@ -72,10 +66,6 @@ export const AppShell = {
                 store.errorMessage
                     ? h('div', { class: 'se-error', style: 'margin:0' }, store.errorMessage)
                     : null,
-
-                showImport.value
-                    ? h(ImportDialog, { store, onClose: () => { showImport.value = false; } })
-                    : null,
             ]);
         };
     },