Why

The hooks feature flag should use the concise canonical name hooks, while existing configs that still use codex_hooks continue to work during the rename.

What

• change the canonical Feature::CodexHooks key from codex_hooks to hooks
• register codex_hooks through the existing legacy-alias path
• update the config schema and canonical config fixtures to prefer hooks
• add regression coverage that both hooks and codex_hooks resolve to Feature::CodexHooks

Verification

• cargo test -p codex-features
• cargo test -p codex-core config::schema_tests
• cargo test -p codex-core pre_tool_use_blocks_shell_when_defined_in_config_toml
• cargo test -p codex-app-server hooks_list_uses_each_cwds_effective_feature_enablement