fix(agent-names): use HTTP-header-safe display names and config keys for API calls (#3138)

Display names with parentheses like 'Atlas (Plan Executor)' cause HTTP
header validation errors in x-opencode-agent-name. This was blocking
Atlas/Prometheus from working via /start-work and auto-retry.

Changes:
- Display names: parens -> dashes ('Atlas - Plan Executor')
- Hooks (start-work, no-hephaestus-non-gpt, no-sisyphus-gpt): use
  config keys ('atlas', 'sisyphus', 'hephaestus') for agent API fields
- auto-retry: use config key instead of display name for promptAsync
- agent-override-protection: handle dash-suffix normalization
- Updated all test expectations to match new format

Closes #3138

src/hooks/atlas/index.test.ts

@@ -1817,10 +1817,10 @@ session_id: ses_untrusted_999
         started_at: "2026-01-02T10:00:00Z",
         session_ids: [MAIN_SESSION_ID],
         plan_name: "test-plan",
-        agent: "Atlas (Plan Executor)",
+        agent: "Atlas - Plan Executor",
       }
       writeBoulderState(TEST_DIR, state)
-      registerAgentName("Atlas (Plan Executor)")
+      registerAgentName("Atlas - Plan Executor")
 
       const mockInput = createMockPluginInput()
       const hook = createAtlasHook(mockInput)
@@ -1836,7 +1836,7 @@ session_id: ses_untrusted_999
       // then
       expect(mockInput._promptMock).toHaveBeenCalled()
       const callArgs = mockInput._promptMock.mock.calls[0][0]
-      expect(callArgs.body.agent).toBe("Atlas (Plan Executor)")
+      expect(callArgs.body.agent).toBe("Atlas - Plan Executor")
       expect(callArgs.body.agent).not.toBe("atlas")
     })