test(plugins): comprehensive plugin system tests and improvements (#19)

* test(cortex-cli): add comprehensive tests for plugin_cmd.rs CLI commands

* test(cortex-plugins): add comprehensive edge case tests

Add tests covering:
- Malformed manifests (empty ID, invalid semver, bad TOML syntax)
- Invalid characters in plugin ID
- Permission and hook execution edge cases
- Hook priority ordering and abort/skip/continue behavior
- Registry SSRF protection (private IPs, metadata endpoints)
- Directory traversal protection
- Plugin registration/unregistration lifecycle
- Configuration edge cases (enable/disable, whitelist mode)
- Error handling and display messages
- Plugin state transitions
- Remote registry management
- Signing and checksum verification

59 tests pass covering error handling and boundary conditions.

* test(cortex-plugins): add lifecycle tests and fix clippy warning

- Add comprehensive lifecycle tests covering plugin discover → load → init → hook → shutdown flow
- Add tests for PluginManager creation, discovery, loading, and lifecycle management
- Add tests for WasmRuntime and WasmPlugin
- Add tests for PluginConfig settings
- Add tests for HookRegistry and HookDispatcher
- Add tests for EventBus and event subscription
- Add tests for PluginCommand and command registry
- Fix clippy warning: replace vec![] with array for constant case list

* test(cortex-plugins): add comprehensive integration tests for plugin system

- Add integration tests for SDK code generation (manifest, Rust, Cargo.toml, TypeScript)
- Add hook system integration tests (priority ordering, abort behavior, session hooks)
- Add command registry tests (categories, aliases, execution with args)
- Add plugin signing/checksum verification tests
- Add plugin context builder tests
- Add manifest parsing tests with all capabilities, WASM settings, dependencies, and hooks
- Add error handling tests for all error variants
- Add registry integration tests for plugin lifecycle

Total test count: 274 tests (108 unit + 59 edge case + 78 lifecycle + 29 integration)

Author: echobt