fix(e2e): update 5 selectors that drifted with FlowPilot/PSA UI changes

Mechanical drift between the e2e selectors and the current UI surfaced
on the first CI run after PR #149 unblocked the artifact upload step.
Five tests, three categories of drift:

1. **Page heading renames** (navigation.spec.ts)
   - `Sessions` → `Session History` on /sessions
   - `Account Settings` → `Account Management` on /account

2. **Route rename** (command-palette.spec.ts:74)
   - The "Troubleshoot with FlowPilot" command palette option now lands
     on /pilot (Phase 1 of the FlowPilot migration renamed /assistant).
     /assistant still 301-redirects, so the assertion accepts either.

3. **Feature moved to /sessions** (history.spec.ts, resume.spec.ts)
   - Default tab on /sessions is "AI Sessions"; flow-session filtering
     and the Resume button moved behind the "Flow Sessions" tab. Both
     tests now click that tab before asserting.
   - resume.spec.ts no longer starts at /trees (Resume buttons aren't
     rendered there anymore — the flow lives on /sessions). Destination
     URL (/trees/:id/navigate) is unchanged.

No product-code changes — these are pure test updates against the
shipped UI. Run the suite locally with
`cd frontend && npm run test:e2e` once a fresh build is available.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/e2e/navigation.spec.ts

@@ -14,7 +14,7 @@ test.describe('authenticated navigation smoke tests', () => {
     await page.goto('/sessions')
 
     await expect(
-      page.getByRole('heading', { name: 'Sessions', exact: true }),
+      page.getByRole('heading', { name: 'Session History', exact: true }),
     ).toBeVisible()
   })
 
@@ -30,7 +30,7 @@ test.describe('authenticated navigation smoke tests', () => {
     await page.goto('/account')
 
     await expect(
-      page.getByRole('heading', { name: 'Account Settings' }),
+      page.getByRole('heading', { name: 'Account Management' }),
     ).toBeVisible()
   })
 })