Add Mega-Debrid multi-account support with automatic fallback

Multiple Mega-Debrid accounts can now be configured as login:password
pairs (one per line). When an account hits Fair-Use limits or errors,
the next account is tried automatically.

- New parser module mega-debrid-accounts.ts (parse, ID generation,
  masking, serialization)
- Per-account daily limits, usage tracking, enable/disable
- Account rotation with per-mode cooldowns (API failures don't
  block Web attempts)
- Backward compatible: existing single megaLogin/megaPassword
  is auto-migrated to the new format
- UI: textarea for credentials, account list with masked logins

Follows the existing Debrid-Link multi-key pattern.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/shared/mega-debrid-accounts.ts

@@ -0,0 +1,96 @@
+export interface MegaDebridAccountEntry {
+  id: string;
+  login: string;
+  password: string;
+  index: number;
+  label: string;
+  maskedLogin: string;
+}
+
+const FNV64_OFFSET_BASIS = 0xcbf29ce484222325n;
+const FNV64_PRIME = 0x100000001b3n;
+const FNV64_MASK = 0xffffffffffffffffn;
+
+function fnv1a64(text: string): string {
+  let hash = FNV64_OFFSET_BASIS;
+  for (const char of text) {
+    hash ^= BigInt(char.codePointAt(0) || 0);
+    hash = (hash * FNV64_PRIME) & FNV64_MASK;
+  }
+  return hash.toString(36);
+}
+
+export function getMegaDebridAccountId(login: string): string {
+  return `mda_${fnv1a64(login.trim().toLowerCase())}`;
+}
+
+export function maskMegaDebridLogin(login: string): string {
+  const trimmed = login.trim();
+  if (!trimmed) {
+    return "Nicht hinterlegt";
+  }
+  if (trimmed.length <= 4) {
+    return `${trimmed[0]}${"*".repeat(trimmed.length - 1)}`;
+  }
+  return `${trimmed.slice(0, 2)}${"*".repeat(Math.max(3, trimmed.length - 4))}${trimmed.slice(-2)}`;
+}
+
+export function getMegaDebridAccountLabel(index: number): string {
+  return `Account ${index + 1}`;
+}
+
+/**
+ * Parse newline-separated "login:password" pairs.
+ * Falls back to treating the entire string as a single login if no colon
+ * is found (backward compat with old megaLogin field).
+ */
+export function parseMegaDebridAccounts(raw: string, legacyPassword = ""): MegaDebridAccountEntry[] {
+  const seen = new Set<string>();
+  const lines = String(raw || "")
+    .split(/\n+/)
+    .map((line) => line.trim())
+    .filter(Boolean);
+
+  const entries: MegaDebridAccountEntry[] = [];
+  for (const line of lines) {
+    const colonIdx = line.indexOf(":");
+    let login: string;
+    let password: string;
+    if (colonIdx >= 0) {
+      login = line.slice(0, colonIdx).trim();
+      password = line.slice(colonIdx + 1).trim();
+    } else {
+      // Legacy format: just a login, use the provided fallback password
+      login = line;
+      password = legacyPassword;
+    }
+    if (!login || !password) {
+      continue;
+    }
+    const key = login.toLowerCase();
+    if (seen.has(key)) {
+      continue;
+    }
+    seen.add(key);
+    entries.push({
+      id: getMegaDebridAccountId(login),
+      login,
+      password,
+      index: entries.length,
+      label: getMegaDebridAccountLabel(entries.length),
+      maskedLogin: maskMegaDebridLogin(login)
+    });
+  }
+  return entries;
+}
+
+export function serializeMegaDebridAccounts(accounts: { login: string; password: string }[]): string {
+  return accounts
+    .filter((a) => a.login.trim() && a.password.trim())
+    .map((a) => `${a.login.trim()}:${a.password.trim()}`)
+    .join("\n");
+}
+
+export function getMegaDebridAccountIds(raw: string, legacyPassword = ""): string[] {
+  return parseMegaDebridAccounts(raw, legacyPassword).map((entry) => entry.id);
+}