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]>

tests/config_round_trip.rs

@@ -12,6 +12,11 @@ use tempfile::tempdir;
 
 use ironclaw::bootstrap::{save_bootstrap_env_to, upsert_bootstrap_var_to};
 
+/// Fake OpenAI API key for test use only. Mirrors the internal
+/// `TEST_OPENAI_API_KEY_LONG` constant from the main crate, which is not
+/// directly available to integration tests due to `#[cfg(test)]`.
+const TEST_OPENAI_API_KEY_LONG: &str = "sk-test-key-1234567890";
+
 /// Parse a .env file into a HashMap using dotenvy.
 fn read_env_map(path: &std::path::Path) -> HashMap<String, String> {
     dotenvy::from_path_iter(path)
@@ -77,7 +82,7 @@ fn bootstrap_env_round_trips_embedding_disabled() {
         &[
             ("DATABASE_BACKEND", "libsql"),
             ("EMBEDDING_ENABLED", "false"),
-            ("OPENAI_API_KEY", "sk-test-key-1234567890"),
+            ("OPENAI_API_KEY", TEST_OPENAI_API_KEY_LONG),
             ("ONBOARD_COMPLETED", "true"),
         ],
     )
@@ -92,7 +97,7 @@ fn bootstrap_env_round_trips_embedding_disabled() {
     );
     assert_eq!(
         map.get("OPENAI_API_KEY").map(String::as_str),
-        Some("sk-test-key-1234567890"),
+        Some(TEST_OPENAI_API_KEY_LONG),
         "OPENAI_API_KEY must be preserved alongside EMBEDDING_ENABLED"
     );
 }