security: fix all review findings, bump to 1.0.19 (build 20)

CRITICAL
- SftpProvider: replace PromiscuousVerifier with TofuHostKeyVerifier
  (trust-on-first-use; stores SHA-256 fingerprints in EncryptedSharedPreferences;
  rejects key changes on subsequent connections)

HIGH
- GoogleDriveProvider: replace raw string interpolation with buildJsonObject
  in uploadFile, createDirectory, and moveFile to prevent JSON injection
- DropboxProvider: replace all raw JSON strings and Dropbox-API-Arg headers
  with buildJsonObject for the same reason
- OAuthHelper: add cryptographically random state parameter to Dropbox and
  OneDrive authorization URLs (stored alongside the PKCE verifier)
- OAuthRedirectActivity: validate returned state against stored value before
  exchanging the authorization code (CSRF protection)

MEDIUM
- WebDavProvider: block cross-host redirects in the manual redirect interceptor
  so Authorization headers are never forwarded to a different server
- AccountSetupScreen: set FLAG_SECURE on the window while credential fields
  are visible to prevent screenshots and screen-recording capture
- libs.versions.toml: security-crypto alpha06 → stable 1.0.0;
  biometric-ktx alpha05 → biometric 1.1.0 (stable, non-ktx artifact matches
  the BiometricManager/BiometricPrompt API actually used in MainActivity)
- CredentialStore: migrate to security-crypto 1.0.0 API (MasterKeys.getOrCreate
  + positional create() args); add saveHostKey/getHostFingerprint for SFTP TOFU

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

gradle/libs.versions.toml

@@ -28,8 +28,8 @@ localbroadcastmanager = "1.1.0"
 coil = "2.7.0"
 splashscreen = "1.0.1"
 timber = "5.0.1"
-securityCrypto = "1.1.0-alpha06"
-biometric = "1.2.0-alpha05"
+securityCrypto = "1.0.0"
+biometric = "1.1.0"
 junit = "4.13.2"
 androidxTestExt = "1.2.1"
 espresso = "3.6.1"
@@ -106,7 +106,7 @@ coil-compose = { group = "io.coil-kt", name = "coil-compose", version.ref = "coi
 
 # Security
 security-crypto = { group = "androidx.security", name = "security-crypto", version.ref = "securityCrypto" }
-biometric = { group = "androidx.biometric", name = "biometric-ktx", version.ref = "biometric" }
+biometric = { group = "androidx.biometric", name = "biometric", version.ref = "biometric" }
 
 # Logging
 timber = { group = "com.jakewharton.timber", name = "timber", version.ref = "timber" }