fix(tests): green warp-app on linux/macOS/windows

[BunsDev]

Summary

Fixes 8 failing tests across the warp-app suite. Failures split into three categories:

1. Brand / rebrand drift

Assertions still pinned to upstream "Warp" copy after the CastCodes rebrand.

• context_chips::display_chip::tests::test_format_git_branch_command_reports_missing_linked_worktree_path — error string now expects CastCodes instead of Warp.
• settings_view::environments_page::tests::test_render_list_page_with_personal_and_team_environments_shows_section_headers — section header expects SHARED BY CASTCODES AND ....

2. Cross-platform path / OS gates

• ai::blocklist::handoff::touched_repos::tests — /repo and /repo/subdir are not absolute on Windows, so Path::is_absolute() rejected them and the touched-path collector dropped the cwd entry. Swap the literals for a cfg(windows)-aware REPO_ROOT / REPO_SUBDIR constant (C:\repo on Windows, /repo elsewhere).
• launch_mode_tests::castcodes_app_bundle_executable_launches_gui — the bundle-detection branch this test exercises (is_macos_app_bundle_executable) is macOS-only; on Linux/Windows it returns false and should_run_as_cli falls through, breaking the assertion. Gated with #[cfg(target_os = "macos")].

3. Drift from production-code changes (OSS / fork-local guards + harness gating)

• ai::blocklist::action_model::execute::start_agent::tests::execute_returns_error_when_local_harness_child_requires_orchestration_v2 — "codex" no longer parses as a valid local-harness child, so parsing failed before the test could reach the OrchestrationV2 gate. Switched to "claude" so parsing succeeds.
• drive::import::modal_body::import_tests::test_expand_directories — three new theme fixtures (tweakcn_sample_dark.yaml, tweakcn_sample_light.yaml, ui_block_theme.yaml) were added to crates/integration/tests/data/. Updated the snapshot to include them.
• pane_group::tests::test_start_shared_session_from_modal — open_share_session_modal now early-returns when cloud_services_available() is false, which is the case on the default OSS channel used in unit-test builds. Added a #[cfg(feature = "test-util")] RAII guard ChannelState::override_channel_for_test(Channel) in warp_core and used it to flip the test into a hosted channel for its duration. The production OSS fork-local gate is preserved.
• auth::auth_manager::auth_manager_test::test_stale_state_when_logged_out_emits_invalid_state_parameter and test_mismatched_state_with_different_user_uid_emits_invalid_state_parameter — initialize_user_from_auth_payload was bailing on hosted_auth_disabled before running CSRF state validation, so the InvalidStateParameter event the tests assert on never fired in OSS builds. Reordered: CSRF state validation runs first (it consumes a locally-generated pending-state token and never touches the hosted backend, so it's safe to run regardless of channel), then the hosted-auth-disabled bail happens before any auth_client interaction.

Test plan

• cargo nextest run -p warp-app --no-fail-fast — 4212 passed, 7 skipped, 1 pre-existing failure: settings::init::tests::test_migration_does_not_rerun_when_marker_present. This test reads ~/.cast-codes/settings.toml directly from the real home dir (not sandboxed) and fails on any machine that has actually used CastCodes. Reproduces on main unchanged — out of scope for this PR.
• cargo fmt --check clean.
• CI clippy will likely flag a pre-existing clippy::unnecessary_unwrap in crates/warpui_core/src/elements/hoverable.rs:661 (also on main, also out of scope).
• CI Linux + Windows runs.

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