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/features/tmux-subagent/cleanup.ts

@@ -1,42 +0,0 @@
-import type { TmuxConfig } from "../../config/schema"
-import { log } from "../../shared"
-import type { TrackedSession } from "./types"
-import { queryWindowState } from "./pane-state-querier"
-import { executeAction } from "./action-executor"
-
-export async function cleanupTmuxSessions(params: {
-  tmuxConfig: TmuxConfig
-  serverUrl: string
-  sourcePaneId: string | undefined
-  sessions: Map<string, TrackedSession>
-  stopPolling: () => void
-}): Promise<void> {
-  params.stopPolling()
-
-  if (params.sessions.size === 0) {
-    log("[tmux-session-manager] cleanup complete")
-    return
-  }
-
-  log("[tmux-session-manager] closing all panes", { count: params.sessions.size })
-  const state = params.sourcePaneId ? await queryWindowState(params.sourcePaneId) : null
-
-  if (state) {
-    const closePromises = Array.from(params.sessions.values()).map((tracked) =>
-      executeAction(
-        { type: "close", paneId: tracked.paneId, sessionId: tracked.sessionId },
-        { config: params.tmuxConfig, serverUrl: params.serverUrl, windowState: state },
-      ).catch((error) =>
-        log("[tmux-session-manager] cleanup error for pane", {
-          paneId: tracked.paneId,
-          error: String(error),
-        }),
-      ),
-    )
-
-    await Promise.all(closePromises)
-  }
-
-  params.sessions.clear()
-  log("[tmux-session-manager] cleanup complete")
-}