PR Vision v0.2.3: UI-editable provider API key, encrypted + write-only

Add PRV_Key_Store (resolver), PRV_Crypto_Helper (libsodium/OpenSSL),
PRV_Key_Manager_Renderer (write-only Settings card), PRV_Key_Test_Ajax.

Key resolver: PRV_OPENROUTER_API_KEY constant > prv_provider_key_enc
option > none. All probe + test paths read key through PRV_Key_Store::get_key().

Security:
- Ciphertext only in prv_provider_key_enc (hex nonce:hex ciphertext).
- Enc key from SHA-256(AUTH_KEY+SECURE_AUTH_KEY) — never stored.
- Plaintext never in options, logs, exceptions, page source, REST, or JS.
- manage_options + nonce on set/remove/test. wp-config precedence enforced.
- write-only UI: password input always renders empty; status text only.
- uninstall.php prv_ wildcard DELETE covers prv_provider_key_enc.

Files: 4 new (all ≤300 lines), 14 modified. Tests: test-key-store.php
(encrypt/decrypt round-trip, wrong-key fails silently, resolver precedence,
write-only render, Remove, constant wins). ARCHITECTURE/CONVENTIONS/CONTEXT/
CHANGELOG all updated in this commit.

Agent-Session: 2026-06-15-pr-vision-v0.2.3-api-key-ui

tests/bootstrap.php

@@ -27,7 +27,7 @@ if ( ! defined( 'ARRAY_N' ) ) {
 	define( 'ARRAY_N', 'ARRAY_N' );
 }
 
-define( 'PRV_VERSION', '0.2.1' );
+define( 'PRV_VERSION', '0.2.3' );
 define( 'PRV_PLUGIN_FILE', __DIR__ . '/../pr-vision.php' );
 define( 'PRV_PLUGIN_DIR', realpath( __DIR__ . '/..' ) . '/' );
 define( 'PRV_PLUGIN_URL', 'http://example.test/wp-content/plugins/pr-vision/' );