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/runtime-fallback/index.test.ts

@@ -2458,7 +2458,7 @@ describe("runtime-fallback", () => {
 
       expect(promptCalls.length).toBe(1)
       const callBody = promptCalls[0]?.body as Record<string, unknown>
-      expect(callBody?.agent).toBe("Prometheus (Plan Builder)")
+      expect(callBody?.agent).toBe("prometheus")
       expect(callBody?.model).toEqual({ providerID: "github-copilot", modelID: "claude-opus-4.6" })
     })
   })