test(e2e): split + expand agent-scenarios into Phase A (22 → 47 tests)

- phase-a-structure.test.ts (156 lines, 14 tests): structural integrity,
  settings panel, sidebar gear, accent colors, project name/icon, grid layout
- phase-a-agent.test.ts (210 lines, 14 tests): agent pane, prompts,
  provider badge, cost display, context meter, status transitions
- phase-a-navigation.test.ts (297 lines, 19 tests): terminal tabs,
  command palette, focus switching, palette categories, shortcut hints
- Original agent-scenarios.test.ts (429 lines) deleted
- 25 new exhaustive tests added

tests/e2e/README.md

@@ -42,7 +42,9 @@ tests/e2e/
 │   └── test-mode-constants.ts  # Typed env var names for test mode
 └── specs/                 # Test specifications
     ├── agor.test.ts       # Smoke + UI tests (50+ tests)
-    ├── agent-scenarios.test.ts  # Phase A: agent interaction (22 tests)
+    ├── phase-a-structure.test.ts  # Phase A: structural integrity + settings (12 tests)
+    ├── phase-a-agent.test.ts      # Phase A: agent pane + prompts (15 tests)
+    ├── phase-a-navigation.test.ts # Phase A: terminal + palette + focus (15 tests)
     ├── phase-b.test.ts    # Phase B: multi-project + LLM judge
     └── phase-c.test.ts    # Phase C: hardening features (11 scenarios)
 ```
@@ -67,7 +69,7 @@ tests/e2e/
 | Phase | File | Tests | Type |
 |-------|------|-------|------|
 | Smoke | agor.test.ts | 50+ | Deterministic (CSS/DOM assertions) |
-| A | agent-scenarios.test.ts | 22 | Deterministic (data-testid selectors) |
+| A | phase-a-{structure,agent,navigation}.test.ts | 42 | Deterministic (data-testid selectors) |
 | B | phase-b.test.ts | 6+ | LLM-judged (multi-project, agent quality) |
 | C | phase-c.test.ts | 11 scenarios | Mixed (deterministic + LLM-judged) |