fix(uitests): stop logging out after every authenticated test

All 7 authenticated-flow XCTestCase classes logged out for real in
tearDown, forcing a real OTP round trip against the production backend
on the next authenticated test. Under CI's back-to-back suite run this
produced ~9 real logins to the same QA phone number in ~9 minutes -
the first few succeeded (~30-40s each) but every one after that failed
to complete within timeout, cascading into 'Login never completed'
across CartCheckoutFlowTests, HomeFiltersFlowTests,
OrderDetailsFlowTests, SavedCardsFlowTests, UserProfileFlowTests.

Removed the per-test logout so the QA account's Keychain-backed session
persists across the whole suite (ensureLoggedIn already no-ops when
already authenticated). Moved the 'must start logged out' guarantee to
the two classes that actually need it - HomeGuestFlowTests and
ProfileLoggedOutFlowTests now force logout themselves right after
app.launch() via a small launch helper, instead of relying on whichever
authenticated class happened to run last.

See decisions/2026-09-11-ui-test-shared-login-session.md.

PediFoodsUITests/AuthenticatedSessionFlowTests.swift

@@ -2,17 +2,14 @@ import XCTest
 
 /// Covers a real, authenticated session with the standing QA account (see
 /// TestFixtures.swift / decisions/2026-08-06-ui-test-account-and-app-attest-bypass.md).
-/// Logs out in tearDown so guest-only tests elsewhere in the same run don't
-/// inherit an authenticated Keychain session.
+/// No per-test logout - the Keychain session is meant to persist across
+/// authenticated-flow tests in the same run; see
+/// decisions/2026-09-11-ui-test-shared-login-session.md.
 final class AuthenticatedSessionFlowTests: XCTestCase {
     override func setUpWithError() throws {
         continueAfterFailure = false
     }
 
-    override func tearDownWithError() throws {
-        XCUIApplication().logoutIfAuthenticated()
-    }
-
     func testLoginReachesAuthenticatedProfile() throws {
         let app = XCUIApplication()
         app.launch()