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/tools/delegate-task/resolve-call-id.test.ts

@@ -1,40 +0,0 @@
-import { describe, test, expect } from "bun:test"
-import { resolveCallID } from "./resolve-call-id"
-import type { ToolContextWithMetadata } from "./types"
-
-describe("resolveCallID", () => {
-  function makeCtx(overrides: Partial<ToolContextWithMetadata> = {}): ToolContextWithMetadata {
-    return {
-      sessionID: "ses_test",
-      messageID: "msg_test",
-      agent: "sisyphus",
-      abort: new AbortController().signal,
-      ...overrides,
-    }
-  }
-
-  test("#given callID is set #then returns callID", () => {
-    const ctx = makeCtx({ callID: "call_abc" })
-    expect(resolveCallID(ctx)).toBe("call_abc")
-  })
-
-  test("#given only callId is set #then returns callId", () => {
-    const ctx = makeCtx({ callId: "call_def" })
-    expect(resolveCallID(ctx)).toBe("call_def")
-  })
-
-  test("#given only call_id is set #then returns call_id", () => {
-    const ctx = makeCtx({ call_id: "call_ghi" })
-    expect(resolveCallID(ctx)).toBe("call_ghi")
-  })
-
-  test("#given callID and callId are both set #then prefers callID", () => {
-    const ctx = makeCtx({ callID: "preferred", callId: "fallback" })
-    expect(resolveCallID(ctx)).toBe("preferred")
-  })
-
-  test("#given no call ID variants are set #then returns undefined", () => {
-    const ctx = makeCtx()
-    expect(resolveCallID(ctx)).toBeUndefined()
-  })
-})