fix: Phase 2 QA — all 25 remaining HIGH/MEDIUM/LOW issues

HIGH fixes (7):
- H1: VNCdirectory admin i18n — 30+ translation keys added
- H2: handleSave try/catch with error toast
- H3: Free/busy accountId scoping
- H4: cancelEventBookings filter by eventId
- H5: Resource picker static apiFetch import
- H6: Sharing-store toast messages via lastMessage state
- H7: roleLabel for all resource types

MEDIUM fixes (11):
- M1: identitySignatureMap cleanup on delete
- M2: Now-line relative positioning
- M3: Radial menu disabled item keyboard nav
- M4: Radial menu stable event listener via refs
- M5: cancelBooking error on missing booking
- M6: PasswordRow isMasked state flag
- M7: Extract shared rights into lib/sharing-rights.ts
- M8: VNCtalk client server-side guard
- M9: Collabora configManager instead of process.env
- M10: CONFIG_ENV_MAP VNCdirectory fields
- M11: SENSITIVE_CONFIG_KEYS field name unification

LOW fixes (7):
- L1-L3: Unused imports removed
- L4: aria-labels on close, clear, search, spinner
- L5-L7: Comments for intentional patterns, null guard

lib/email-import.ts

@@ -1,5 +1,4 @@
 import type { IJMAPClient } from "@/lib/jmap/client-interface";
-import type { Mailbox } from "@/lib/jmap/types";
 import { expandImportableEmails } from "@/lib/eml-import";
 
 export type ConflictResolution = "skip" | "replace" | "copy";
@@ -20,15 +19,6 @@ export interface ImportResult {
   errors: Array<{ file: string; error: string }>;
 }
 
-function toBase64(buffer: ArrayBuffer): string {
-  let binary = "";
-  const bytes = new Uint8Array(buffer);
-  for (let i = 0; i < bytes.byteLength; i++) {
-    binary += String.fromCharCode(bytes[i]);
-  }
-  return btoa(binary);
-}
-
 interface ParsedEml {
   messageId: string | null;
   subject: string;