fix: remove dead-code files accidentally resurrected by previous commit

The previous commit (2dfa6336f) used 'git add -A' which swept up files that
prior commits had intentionally deleted but were still present untracked in
the local workspace. This commit re-deletes them to match the upstream intent.

Files removed (each was previously deleted in the cited commit):

- drafts/gpt-5-5/{README,deep,hephaestus,oracle,sisyphus-junior,sisyphus}.md
  (deleted in 40ded422c chore(drafts): remove stale gpt-5.5 prompt drafts)
- src/plugin-dispose.{ts,test.ts}
  (deleted in e2f5c0d36 refactor(plugin): remove orphaned createPluginDispose)
- src/features/tmux-subagent/{cleanup,session-created-handler,session-deleted-handler}.ts
  (deleted in 7a7926f22 chore(tmux-subagent): remove dead event-handler modules)
- src/tools/delegate-task/{model-string-parser,resolve-call-id,resolve-call-id.test}.ts
  (model-string-parser deleted in db056346d; resolve-call-id was scratch)
- src/__debug-test.test.ts (debug scratch never intended for git)

Typecheck + model-requirements tests still pass. The legitimate metis +
AGENTS.md edits from the previous commit remain on dev.

src/plugin-dispose.ts

@@ -1,51 +0,0 @@
-import { log } from "./shared"
-
-export type PluginDispose = () => Promise<void>
-
-export function createPluginDispose(args: {
-  backgroundManager: {
-    shutdown: () => void | Promise<void>
-  }
-  skillMcpManager: {
-    disconnectAll: () => Promise<void>
-  }
-  lspManager: {
-    stopAll: () => Promise<void>
-  }
-  disposeHooks: () => void
-}): PluginDispose {
-  const { backgroundManager, skillMcpManager, lspManager, disposeHooks } = args
-  let disposePromise: Promise<void> | null = null
-
-  return async (): Promise<void> => {
-    if (disposePromise) {
-      await disposePromise
-      return
-    }
-
-    disposePromise = (async (): Promise<void> => {
-      try {
-        await backgroundManager.shutdown()
-      } catch (error) {
-        log("[plugin-dispose] backgroundManager.shutdown() error:", error)
-      }
-      try {
-        await skillMcpManager.disconnectAll()
-      } catch (error) {
-        log("[plugin-dispose] skillMcpManager.disconnectAll() error:", error)
-      }
-      try {
-        await lspManager.stopAll()
-      } catch (error) {
-        log("[plugin-dispose] lspManager.stopAll() error:", error)
-      }
-      try {
-        disposeHooks()
-      } catch (error) {
-        log("[plugin-dispose] disposeHooks() error:", error)
-      }
-    })()
-
-    await disposePromise
-  }
-}