refactor: remove dead ultrawork model override code

Remove ultrawork-model-override hook and per-agent ultrawork model swap
config that relied on zen opencode.ai free tier (no longer functional).

Removed:
- src/hooks/ultrawork-model-override/ (hook, test, index)
- ultrawork field from AgentOverrideConfigSchema
- ultrawork-model-override from HookNameSchema
- UltraworkConfig type from model-fallback-types
- Non-max20 sonnet+ultrawork-opus codepath from model-fallback
- Claude subscription model table from installation docs
- All references in plugin-interface, create-session-hooks, schema.json
- Related test cases and updated snapshots

src/plugin/hooks/create-session-hooks.ts

@@ -25,7 +25,6 @@ import {
   createPreemptiveCompactionHook,
 } from "../../hooks"
 import { createAnthropicEffortHook } from "../../hooks/anthropic-effort"
-import { createUltraworkModelOverrideHook } from "../../hooks/ultrawork-model-override"
 import {
   detectExternalNotificationPlugin,
   getNotificationConflictWarning,
@@ -56,7 +55,6 @@ export type SessionHooks = {
   questionLabelTruncator: ReturnType<typeof createQuestionLabelTruncatorHook>
   taskResumeInfo: ReturnType<typeof createTaskResumeInfoHook>
   anthropicEffort: ReturnType<typeof createAnthropicEffortHook> | null
-  ultraworkModelOverride: ReturnType<typeof createUltraworkModelOverrideHook> | null
 }
 
 export function createSessionHooks(args: {
@@ -171,10 +169,6 @@ export function createSessionHooks(args: {
     ? safeHook("anthropic-effort", () => createAnthropicEffortHook())
     : null
 
-  const ultraworkModelOverride = isHookEnabled("ultrawork-model-override")
-    ? safeHook("ultrawork-model-override", () => createUltraworkModelOverrideHook({ agents: pluginConfig.agents }))
-    : null
-
   return {
     contextWindowMonitor,
     preemptiveCompaction,
@@ -197,6 +191,5 @@ export function createSessionHooks(args: {
     questionLabelTruncator,
     taskResumeInfo,
     anthropicEffort,
-    ultraworkModelOverride,
   }
 }