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/model-string-parser.ts

@@ -1,63 +0,0 @@
-const KNOWN_VARIANTS = new Set([
-  "low",
-  "medium",
-  "high",
-  "xhigh",
-  "max",
-  "minimal",
-  "none",
-  "auto",
-  "thinking",
-])
-
-export function parseVariantFromModelID(rawModelID: string): { modelID: string; variant?: string } {
-  const trimmedModelID = rawModelID.trim()
-  if (!trimmedModelID) {
-    return { modelID: "" }
-  }
-
-  const parenthesizedVariant = trimmedModelID.match(/^(.*)\(([^()]+)\)\s*$/)
-  if (parenthesizedVariant) {
-    const modelID = parenthesizedVariant[1]?.trim() ?? ""
-    const variant = parenthesizedVariant[2]?.trim()
-    return variant ? { modelID, variant } : { modelID }
-  }
-
-  const spaceVariant = trimmedModelID.match(/^(.*\S)\s+([a-z][a-z0-9_-]*)$/i)
-  if (spaceVariant) {
-    const modelID = spaceVariant[1]?.trim() ?? ""
-    const variant = spaceVariant[2]?.trim().toLowerCase()
-    if (variant && KNOWN_VARIANTS.has(variant)) {
-      return { modelID, variant }
-    }
-  }
-
-  return { modelID: trimmedModelID }
-}
-
-export function parseModelString(
-  model: string,
-): { providerID: string; modelID: string; variant?: string } | undefined {
-  const trimmedModel = model.trim()
-  if (!trimmedModel) return undefined
-
-  const parts = trimmedModel.split("/")
-  if (parts.length < 2) {
-    return undefined
-  }
-
-  const providerID = parts[0]?.trim()
-  const rawModelID = parts.slice(1).join("/").trim()
-  if (!providerID || !rawModelID) {
-    return undefined
-  }
-
-  const parsedModel = parseVariantFromModelID(rawModelID)
-  if (!parsedModel.modelID) {
-    return undefined
-  }
-
-  return parsedModel.variant
-    ? { providerID, modelID: parsedModel.modelID, variant: parsedModel.variant }
-    : { providerID, modelID: parsedModel.modelID }
-}