feat: seedpgp v1.1.0 - BIP39 mnemonic PGP encryption tool

- Implement cv25519 PGP encryption/decryption
- Add Base45 encoding with CRC16 integrity checks
- Create SEEDPGP1 frame format for QR codes
- Support BIP39 passphrase flag indicator
- Add comprehensive test suite with Trezor BIP39 vectors
- 15 passing tests covering all core functionality

src/lib/bip39.ts

@@ -0,0 +1,24 @@
+// Prototype-level BIP39 validation:
+// - enforces allowed word counts
+// - normalizes whitespace/case
+// NOTE: checksum + wordlist membership verification is intentionally omitted here.
+
+export function normalizeBip39Mnemonic(words: string): string {
+    return words.trim().toLowerCase().replace(/\s+/g, " ");
+}
+
+export function validateBip39Mnemonic(words: string): { valid: boolean; error?: string } {
+    const normalized = normalizeBip39Mnemonic(words);
+    const arr = normalized.length ? normalized.split(" ") : [];
+
+    const validCounts = new Set([12, 15, 18, 21, 24]);
+    if (!validCounts.has(arr.length)) {
+        return {
+            valid: false,
+            error: `Invalid word count: ${arr.length}. Must be 12, 15, 18, 21, or 24.`,
+        };
+    }
+
+    // In production: verify each word is in the selected wordlist + verify checksum.
+    return { valid: true };
+}