refactor(plugin): update atlas references

Update plugin handlers, commands, and integration points to use 'atlas' agent name. Start-work command and config handler now reference 'atlas'.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/start-work/index.test.ts

@@ -379,7 +379,7 @@ describe("start-work hook", () => {
   })
 
   describe("session agent management", () => {
-    test("should update session agent to orchestrator-sisyphus when start-work command is triggered", async () => {
+    test("should update session agent to atlas when start-work command is triggered", async () => {
       // #given
       const updateSpy = spyOn(sessionState, "updateSessionAgent")
       
@@ -395,7 +395,7 @@ describe("start-work hook", () => {
       )
 
       // #then
-      expect(updateSpy).toHaveBeenCalledWith("ses-prometheus-to-sisyphus", "orchestrator-sisyphus")
+      expect(updateSpy).toHaveBeenCalledWith("ses-prometheus-to-sisyphus", "atlas")
       updateSpy.mockRestore()
     })
   })

src/hooks/start-work/index.ts

@@ -71,7 +71,7 @@ export function createStartWorkHook(ctx: PluginInput) {
         sessionID: input.sessionID,
       })
 
-      updateSessionAgent(input.sessionID, "orchestrator-sisyphus")
+      updateSessionAgent(input.sessionID, "atlas")
 
       const existingState = readBoulderState(ctx.directory)
       const sessionId = input.sessionID