chore: implement NPM/JSON import routes and fix SMTP persistence

Phase 3 of skipped tests remediation - enables 7 previously skipped E2E tests

Backend:

Add NPM import handler with session-based upload/commit/cancel
Add JSON import handler with Charon/NPM format support
Fix SMTP SaveSMTPConfig using transaction-based upsert
Add comprehensive unit tests for new handlers
Frontend:

Add ImportNPM page component following ImportCaddy pattern
Add ImportJSON page component with format detection
Add useNPMImport and useJSONImport React Query hooks
Add API clients for npm/json import endpoints
Register routes in App.tsx and navigation in Layout.tsx
Add i18n keys for new import pages
Tests:

7 E2E tests now enabled and passing
Backend coverage: 86.8%
Reduced total skipped tests from 98 to 91
Closes: Phase 3 of skipped-tests-remediation plan

frontend/src/api/jsonImport.ts

@@ -0,0 +1,90 @@
+import client from './client';
+
+/** Represents a host parsed from a JSON export. */
+export interface JSONHost {
+  domain_names: string;
+  forward_scheme: string;
+  forward_host: string;
+  forward_port: number;
+  ssl_forced: boolean;
+  websocket_support: boolean;
+}
+
+/** Preview of a JSON import with hosts and conflicts. */
+export interface JSONImportPreview {
+  session: {
+    id: string;
+    state: string;
+    source: string;
+  };
+  preview: {
+    hosts: JSONHost[];
+    conflicts: string[];
+    errors: string[];
+  };
+  conflict_details: Record<string, {
+    existing: {
+      forward_scheme: string;
+      forward_host: string;
+      forward_port: number;
+      ssl_forced: boolean;
+      websocket: boolean;
+      enabled: boolean;
+    };
+    imported: {
+      forward_scheme: string;
+      forward_host: string;
+      forward_port: number;
+      ssl_forced: boolean;
+      websocket: boolean;
+    };
+  }>;
+}
+
+/** Result of committing a JSON import operation. */
+export interface JSONImportCommitResult {
+  created: number;
+  updated: number;
+  skipped: number;
+  errors: string[];
+}
+
+/**
+ * Uploads JSON export content for import preview.
+ * @param content - The JSON export content as a string
+ * @returns Promise resolving to JSONImportPreview with parsed hosts
+ * @throws {AxiosError} If parsing fails or content is invalid
+ */
+export const uploadJSONExport = async (content: string): Promise<JSONImportPreview> => {
+  const { data } = await client.post<JSONImportPreview>('/import/json/upload', { content });
+  return data;
+};
+
+/**
+ * Commits the JSON import, creating/updating proxy hosts.
+ * @param sessionUuid - The import session UUID
+ * @param resolutions - Map of conflict resolutions (domain -> 'keep'|'replace'|'skip')
+ * @param names - Map of custom names for imported hosts
+ * @returns Promise resolving to JSONImportCommitResult with counts
+ * @throws {AxiosError} If commit fails
+ */
+export const commitJSONImport = async (
+  sessionUuid: string,
+  resolutions: Record<string, string>,
+  names: Record<string, string>
+): Promise<JSONImportCommitResult> => {
+  const { data } = await client.post<JSONImportCommitResult>('/import/json/commit', {
+    session_uuid: sessionUuid,
+    resolutions,
+    names,
+  });
+  return data;
+};
+
+/**
+ * Cancels the current JSON import session.
+ * @throws {AxiosError} If cancellation fails
+ */
+export const cancelJSONImport = async (): Promise<void> => {
+  await client.post('/import/json/cancel');
+};

frontend/src/api/npmImport.ts

@@ -0,0 +1,90 @@
+import client from './client';
+
+/** Represents a host parsed from an NPM export. */
+export interface NPMHost {
+  domain_names: string;
+  forward_scheme: string;
+  forward_host: string;
+  forward_port: number;
+  ssl_forced: boolean;
+  websocket_support: boolean;
+}
+
+/** Preview of an NPM import with hosts and conflicts. */
+export interface NPMImportPreview {
+  session: {
+    id: string;
+    state: string;
+    source: string;
+  };
+  preview: {
+    hosts: NPMHost[];
+    conflicts: string[];
+    errors: string[];
+  };
+  conflict_details: Record<string, {
+    existing: {
+      forward_scheme: string;
+      forward_host: string;
+      forward_port: number;
+      ssl_forced: boolean;
+      websocket: boolean;
+      enabled: boolean;
+    };
+    imported: {
+      forward_scheme: string;
+      forward_host: string;
+      forward_port: number;
+      ssl_forced: boolean;
+      websocket: boolean;
+    };
+  }>;
+}
+
+/** Result of committing an NPM import operation. */
+export interface NPMImportCommitResult {
+  created: number;
+  updated: number;
+  skipped: number;
+  errors: string[];
+}
+
+/**
+ * Uploads NPM export content for import preview.
+ * @param content - The NPM export JSON content as a string
+ * @returns Promise resolving to NPMImportPreview with parsed hosts
+ * @throws {AxiosError} If parsing fails or content is invalid
+ */
+export const uploadNPMExport = async (content: string): Promise<NPMImportPreview> => {
+  const { data } = await client.post<NPMImportPreview>('/import/npm/upload', { content });
+  return data;
+};
+
+/**
+ * Commits the NPM import, creating/updating proxy hosts.
+ * @param sessionUuid - The import session UUID
+ * @param resolutions - Map of conflict resolutions (domain -> 'keep'|'replace'|'skip')
+ * @param names - Map of custom names for imported hosts
+ * @returns Promise resolving to NPMImportCommitResult with counts
+ * @throws {AxiosError} If commit fails
+ */
+export const commitNPMImport = async (
+  sessionUuid: string,
+  resolutions: Record<string, string>,
+  names: Record<string, string>
+): Promise<NPMImportCommitResult> => {
+  const { data } = await client.post<NPMImportCommitResult>('/import/npm/commit', {
+    session_uuid: sessionUuid,
+    resolutions,
+    names,
+  });
+  return data;
+};
+
+/**
+ * Cancels the current NPM import session.
+ * @throws {AxiosError} If cancellation fails
+ */
+export const cancelNPMImport = async (): Promise<void> => {
+  await client.post('/import/npm/cancel');
+};