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/session-deleted-handler.ts

@@ -1,50 +0,0 @@
-import type { TmuxConfig } from "../../config/schema"
-import type { TrackedSession } from "./types"
-import { log } from "../../shared"
-import { queryWindowState } from "./pane-state-querier"
-import { decideCloseAction, type SessionMapping } from "./decision-engine"
-import { executeAction } from "./action-executor"
-
-export interface SessionDeletedHandlerDeps {
-  tmuxConfig: TmuxConfig
-  serverUrl: string
-  sourcePaneId: string | undefined
-  sessions: Map<string, TrackedSession>
-  isEnabled: () => boolean
-  getSessionMappings: () => SessionMapping[]
-  stopPolling: () => void
-}
-
-export async function handleSessionDeleted(
-  deps: SessionDeletedHandlerDeps,
-  event: { sessionID: string },
-): Promise<void> {
-  if (!deps.isEnabled()) return
-  if (!deps.sourcePaneId) return
-
-  const tracked = deps.sessions.get(event.sessionID)
-  if (!tracked) return
-
-  log("[tmux-session-manager] onSessionDeleted", { sessionId: event.sessionID })
-
-  const state = await queryWindowState(deps.sourcePaneId)
-  if (!state) {
-    deps.sessions.delete(event.sessionID)
-    return
-  }
-
-  const closeAction = decideCloseAction(state, event.sessionID, deps.getSessionMappings())
-  if (closeAction) {
-    await executeAction(closeAction, {
-      config: deps.tmuxConfig,
-      serverUrl: deps.serverUrl,
-      windowState: state,
-    })
-  }
-
-  deps.sessions.delete(event.sessionID)
-
-  if (deps.sessions.size === 0) {
-    deps.stopPolling()
-  }
-}