test: add e2e coverage and mock backends for jira and linear integrations (#771)

* test: add e2e coverage and mock backends for jira and linear integrations

Adds in-memory MockClient + MockController for both integrations gated by
KANDEV_MOCK_{JIRA,LINEAR}=true, plus apiClient mock helpers and Playwright
specs covering settings and import flows.

Also fixes ValidatedPopover's TriggerButton silently dropping radix Slot's
onClick handler — the popover wouldn't open under any synthetic-click path
(including Playwright). Spreads `...rest` onto the inner Button.

Reworks the integration cleanup hook in test-base as an auto fixture so it
runs for every test using the imported `test` object, not just tests in the
fixture file itself.

* fix: address PR review feedback on jira/linear mocks and e2e specs

- Fix SetAuthResult docstrings: nil simulates an unconfigured state, not the default success.
- Drop unused JSON tags from doneTransitionCall and setStateCall (Go-only test fixtures).
- Track Linear issue insertion order so SearchIssues returns deterministic results instead of map-iteration shuffle.
- Document filterByJQL precedence at the SearchTickets call site so the all-hits-on-no-match fallback is visible.
- Wait for the post-save auth-health probe before forcing a failure in the seeded-failure tests, eliminating a goroutine race.
- Reorder authMethod precedence in setJiraConfig/setLinearConfig to put the spread first so 'caller wins' reads naturally.

---------

Co-authored-by: Kandev Agent <agent@kandev.dev>

apps/backend/internal/linear/service.go

@@ -30,6 +30,16 @@ type Service struct {
 	clientFn  ClientFactory
 	cache     map[string]Client // workspaceID → client, cleared on config change.
 	probeHook func(workspaceID string)
+	// mockClient is non-nil only when Provide built the service with a MockClient
+	// (KANDEV_MOCK_LINEAR=true). Exposed via MockClient() so the e2e control
+	// routes can drive the same instance the clientFn returns.
+	mockClient *MockClient
+}
+
+// MockClient returns the shared mock client when the service was built in mock
+// mode, or nil for production builds.
+func (s *Service) MockClient() *MockClient {
+	return s.mockClient
 }
 
 // ClientFactory builds a Client for the given config + secret. Overridable so