feat: add config portability — full export/import, homepage import, docker label discovery

Add a dedicated Import/Export tool page with full configuration export/import
(v2.0 bundle with encrypted secrets), Homepage services.yaml import with env
variable resolution, and manual Docker label discovery (moved from cron job).

Support importing Homarr JSON during onboarding alongside legacy zip import.

New @homarr/board-portability package handles schema, serialization, compat
checks, and import planning. Shared preview UI reused across admin and onboarding.

Fix xterm.js crash by removing deprecated @xterm/addon-canvas (incompatible
with xterm v6). Fix Homepage env variable i18n and React 19 currentTarget bug.

See docs/config-portability.md for full changelog.

packages/validation/src/board.ts

@@ -94,3 +94,12 @@ export const boardCreateSchema = z.object({
 });
 
 export const boardSavePermissionsSchema = createSavePermissionsSchema(zodEnumFromArray(boardPermissions));
+
+export const boardExportBundleSchema = z.object({
+  id: z.string(),
+});
+
+export const boardImportBundleSchema = z.object({
+  content: z.string().min(1),
+  name: boardNameSchema,
+});