Add password-encrypted vault

- Encrypt stored secret keys with AES-256-GCM under an Argon2id-derived key;
  the vault stays plaintext until a password is set (Settings -> Storage or
  the CLI set-password command)
- Only secret keys are encrypted; labels and npubs stay readable so profiles
  can be browsed while the vault is locked
- Backend: crypto module, Vault.crypto metadata, unlock/lock/set/remove
  password on App, VaultLocked/WrongPassword errors, secret resolution on the
  publish path
- IPC: set_vault_password, unlock_vault, lock_vault, remove_vault_password
- CLI: set-password, remove-password, unlock; create/publish prompt when the
  vault is locked (NFM_PASSWORD env or hidden prompt, never argv)
- GUI: unlock banner + modal on locked vaults, protect/change/remove password
  in Settings, password field styling
- Tests: Rust (argon2/AES round-trips, vault lifecycle) and Vitest (unlock
  flow, set/change/remove password), all green

Cargo.lock

@@ -12,6 +12,31 @@ dependencies = [
  "generic-array",
 ]
 
+[[package]]
+name = "aes"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b169f7a6d4742236a0a00c541b845991d0ac43e546831af1249753ab4c3aa3a0"
+dependencies = [
+ "cfg-if",
+ "cipher",
+ "cpufeatures",
+]
+
+[[package]]
+name = "aes-gcm"
+version = "0.10.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "831010a0f742e1209b3bcea8fab6a8e149051ba6099432c8cb2cc117dec3ead1"
+dependencies = [
+ "aead",
+ "aes",
+ "cipher",
+ "ctr",
+ "ghash",
+ "subtle",
+]
+
 [[package]]
 name = "aho-corasick"
 version = "1.1.5"
@@ -21,6 +46,18 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "argon2"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c3610892ee6e0cbce8ae2700349fcf8f98adb0dbfbee85aec3c9179d29cc072"
+dependencies = [
+ "base64ct",
+ "blake2",
+ "cpufeatures",
+ "password-hash",
+]
+
 [[package]]
 name = "arrayvec"
 version = "0.7.8"
@@ -136,6 +173,15 @@ version = "2.13.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b588b76d00fde79687d7646a9b5bdf3cc0f655e0bbd080335a95d7e96f3587da"
 
+[[package]]
+name = "blake2"
+version = "0.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "46502ad458c9a52b69d4d4d32775c788b7a1b85e8bc9d482d92250fc0e3f8efe"
+dependencies = [
+ "digest",
+]
+
 [[package]]
 name = "block-buffer"
 version = "0.10.4"
@@ -246,6 +292,15 @@ dependencies = [
  "typenum",
 ]
 
+[[package]]
+name = "ctr"
+version = "0.9.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0369ee1ad671834580515889b80f2ea915f23b8be8d0daa4bbaf2ac5c7590835"
+dependencies = [
+ "cipher",
+]
+
 [[package]]
 name = "data-encoding"
 version = "2.11.1"
@@ -415,6 +470,16 @@ dependencies = [
  "r-efi 6.0.0",
 ]
 
+[[package]]
+name = "ghash"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0d8a4362ccb29cb0b265253fb0a2728f592895ee6854fd9bc13f2ffda266ff1"
+dependencies = [
+ "opaque-debug",
+ "polyval",
+]
+
 [[package]]
 name = "gloo-timers"
 version = "0.3.0"
@@ -719,8 +784,13 @@ dependencies = [
 name = "nostr-manager-backend"
 version = "0.1.0"
 dependencies = [
+ "aes-gcm",
+ "argon2",
+ "base64",
+ "getrandom 0.2.17",
  "hex",
  "nostr-sdk",
+ "rpassword",
  "serde",
  "serde_json",
  "tokio",
@@ -838,6 +908,18 @@ dependencies = [
  "universal-hash",
 ]
 
+[[package]]
+name = "polyval"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d1fe60d06143b2430aa532c94cfe9e29783047f06c0d7fd359a9a51b729fa25"
+dependencies = [
+ "cfg-if",
+ "cpufeatures",
+ "opaque-debug",
+ "universal-hash",
+]
+
 [[package]]
 name = "potential_utf"
 version = "0.1.5"
@@ -997,6 +1079,27 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "rpassword"
+version = "7.5.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2da316a15f47e3d053de9cb2c439650bd8fa4aaeb9365f2e5f27f492ff73c196"
+dependencies = [
+ "libc",
+ "rtoolbox",
+ "windows-sys 0.61.2",
+]
+
+[[package]]
+name = "rtoolbox"
+version = "0.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "50a0e551c1e27e1731aba276dbeaeac73f53c7cd34d1bda485d02bd1e0f36844"
+dependencies = [
+ "libc",
+ "windows-sys 0.59.0",
+]
+
 [[package]]
 name = "rustls"
 version = "0.23.43"
@@ -1605,6 +1708,15 @@ dependencies = [
  "windows-targets",
 ]
 
+[[package]]
+name = "windows-sys"
+version = "0.59.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e38bc4d79ed67fd075bcc251a1c39b32a1776bbe92e5bef1f0bf1f8c531853b"
+dependencies = [
+ "windows-targets",
+]
+
 [[package]]
 name = "windows-sys"
 version = "0.61.2"