refactor: centralize test credential constants into testing::credentials (#829)

* refactor: centralize test credential constants into testing::credentials

Scattered test credential strings (API keys, OAuth tokens, crypto keys,
Telegram tokens, session tokens) across ~25 files made security auditing
harder and created unnecessary duplication. Centralize all test-only fake
credentials into a new `src/testing/credentials.rs` module with named
constants and a shared `test_secrets_store()` helper.

- Convert `src/testing.rs` to directory module (`src/testing/mod.rs`)
- Add `src/testing/credentials.rs` with ~30 named constants
- Replace hardcoded literals in 24 source files
- Deduplicate `test_store()` helper (was copy-pasted in 3 files)
- Leave leak_detector/shell/signature tests as-is (inline values
  aid readability for pattern detection tests)

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* refactor: replace real Telegram bot token with obviously fake test stub

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* Update src/testing/credentials.rs

Co-authored-by: Copilot <[email protected]>

* Update src/testing/credentials.rs

Co-authored-by: Copilot <[email protected]>

* refactor: address PR review feedback on test credentials

- Fix TEST_CRYPTO_KEY doc comment ("32-byte hex" → "32-character key string")
- Rename confusing "real"/"fake" Anthropic constant names and values
- Change TEST_STRIPE_KEY from "sk-live" to "sk_test_fake123" to avoid scanners
- Use test_secrets_store() helper in orchestrator and http tool tests
- Clarify config_round_trip.rs doc comment about integration test visibility

Co-Authored-By: Claude Opus 4.6 <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <[email protected]>
Co-authored-by: Copilot <[email protected]>

src/secrets/crypto.rs

@@ -153,11 +153,11 @@ mod tests {
     use secrecy::SecretString;
 
     use crate::secrets::crypto::SecretsCrypto;
+    use crate::testing::credentials::TEST_CRYPTO_KEY;
 
     fn test_crypto() -> SecretsCrypto {
         // 32-byte test key
-        let key = "0123456789abcdef0123456789abcdef";
-        SecretsCrypto::new(SecretString::from(key.to_string())).unwrap()
+        SecretsCrypto::new(SecretString::from(TEST_CRYPTO_KEY.to_string())).unwrap()
     }
 
     #[test]

src/secrets/store.rs

@@ -802,30 +802,25 @@ pub mod in_memory {
 
 #[cfg(test)]
 mod tests {
-    use std::sync::Arc;
-
-    use secrecy::SecretString;
-
-    use crate::secrets::crypto::SecretsCrypto;
     use crate::secrets::store::SecretsStore;
-    use crate::secrets::store::in_memory::InMemorySecretsStore;
     use crate::secrets::types::CreateSecretParams;
+    use crate::testing::credentials::{
+        TEST_OPENAI_API_KEY_SHORT, TEST_SECRET_VALUE, TEST_STRIPE_KEY, test_secrets_store,
+    };
 
-    fn test_store() -> InMemorySecretsStore {
-        let key = "0123456789abcdef0123456789abcdef";
-        let crypto = Arc::new(SecretsCrypto::new(SecretString::from(key.to_string())).unwrap());
-        InMemorySecretsStore::new(crypto)
+    fn test_store() -> crate::secrets::store::in_memory::InMemorySecretsStore {
+        test_secrets_store()
     }
 
     #[tokio::test]
     async fn test_create_and_get() {
         let store = test_store();
-        let params = CreateSecretParams::new("api_key", "sk-test-12345");
+        let params = CreateSecretParams::new("api_key", TEST_SECRET_VALUE);
 
         store.create("user1", params).await.unwrap();
 
         let decrypted = store.get_decrypted("user1", "api_key").await.unwrap();
-        assert_eq!(decrypted.expose(), "sk-test-12345");
+        assert_eq!(decrypted.expose(), TEST_SECRET_VALUE);
     }
 
     #[tokio::test]
@@ -878,11 +873,17 @@ mod tests {
     async fn test_is_accessible() {
         let store = test_store();
         store
-            .create("user1", CreateSecretParams::new("openai_key", "sk-test"))
+            .create(
+                "user1",
+                CreateSecretParams::new("openai_key", TEST_OPENAI_API_KEY_SHORT),
+            )
             .await
             .unwrap();
         store
-            .create("user1", CreateSecretParams::new("stripe_key", "sk-live"))
+            .create(
+                "user1",
+                CreateSecretParams::new("stripe_key", TEST_STRIPE_KEY),
+            )
             .await
             .unwrap();