refactor(cli): split install.ts and model-fallback.ts into focused modules

Install pipeline:
- cli-installer.ts, tui-installer.ts, tui-install-prompts.ts
- install-validators.ts

Model fallback:
- model-fallback-types.ts, fallback-chain-resolution.ts
- provider-availability.ts, provider-model-id-transform.ts

src/cli/tui-install-prompts.ts

@@ -0,0 +1,111 @@
+import * as p from "@clack/prompts"
+import type { Option } from "@clack/prompts"
+import type {
+  ClaudeSubscription,
+  DetectedConfig,
+  InstallConfig,
+} from "./types"
+import { detectedToInitialValues } from "./install-validators"
+
+async function selectOrCancel<TValue extends Readonly<string | boolean | number>>(params: {
+  message: string
+  options: Option<TValue>[]
+  initialValue: TValue
+}): Promise<TValue | null> {
+  const value = await p.select<TValue>({
+    message: params.message,
+    options: params.options,
+    initialValue: params.initialValue,
+  })
+  if (p.isCancel(value)) {
+    p.cancel("Installation cancelled.")
+    return null
+  }
+  return value as TValue
+}
+
+export async function promptInstallConfig(detected: DetectedConfig): Promise<InstallConfig | null> {
+  const initial = detectedToInitialValues(detected)
+
+  const claude = await selectOrCancel<ClaudeSubscription>({
+    message: "Do you have a Claude Pro/Max subscription?",
+    options: [
+      { value: "no", label: "No", hint: "Will use opencode/glm-4.7-free as fallback" },
+      { value: "yes", label: "Yes (standard)", hint: "Claude Opus 4.5 for orchestration" },
+      { value: "max20", label: "Yes (max20 mode)", hint: "Full power with Claude Sonnet 4.5 for Librarian" },
+    ],
+    initialValue: initial.claude,
+  })
+  if (!claude) return null
+
+  const openai = await selectOrCancel({
+    message: "Do you have an OpenAI/ChatGPT Plus subscription?",
+    options: [
+      { value: "no", label: "No", hint: "Oracle will use fallback models" },
+      { value: "yes", label: "Yes", hint: "GPT-5.2 for Oracle (high-IQ debugging)" },
+    ],
+    initialValue: initial.openai,
+  })
+  if (!openai) return null
+
+  const gemini = await selectOrCancel({
+    message: "Will you integrate Google Gemini?",
+    options: [
+      { value: "no", label: "No", hint: "Frontend/docs agents will use fallback" },
+      { value: "yes", label: "Yes", hint: "Beautiful UI generation with Gemini 3 Pro" },
+    ],
+    initialValue: initial.gemini,
+  })
+  if (!gemini) return null
+
+  const copilot = await selectOrCancel({
+    message: "Do you have a GitHub Copilot subscription?",
+    options: [
+      { value: "no", label: "No", hint: "Only native providers will be used" },
+      { value: "yes", label: "Yes", hint: "Fallback option when native providers unavailable" },
+    ],
+    initialValue: initial.copilot,
+  })
+  if (!copilot) return null
+
+  const opencodeZen = await selectOrCancel({
+    message: "Do you have access to OpenCode Zen (opencode/ models)?",
+    options: [
+      { value: "no", label: "No", hint: "Will use other configured providers" },
+      { value: "yes", label: "Yes", hint: "opencode/claude-opus-4-6, opencode/gpt-5.2, etc." },
+    ],
+    initialValue: initial.opencodeZen,
+  })
+  if (!opencodeZen) return null
+
+  const zaiCodingPlan = await selectOrCancel({
+    message: "Do you have a Z.ai Coding Plan subscription?",
+    options: [
+      { value: "no", label: "No", hint: "Will use other configured providers" },
+      { value: "yes", label: "Yes", hint: "Fallback for Librarian and Multimodal Looker" },
+    ],
+    initialValue: initial.zaiCodingPlan,
+  })
+  if (!zaiCodingPlan) return null
+
+  const kimiForCoding = await selectOrCancel({
+    message: "Do you have a Kimi For Coding subscription?",
+    options: [
+      { value: "no", label: "No", hint: "Will use other configured providers" },
+      { value: "yes", label: "Yes", hint: "Kimi K2.5 for Sisyphus/Prometheus fallback" },
+    ],
+    initialValue: initial.kimiForCoding,
+  })
+  if (!kimiForCoding) return null
+
+  return {
+    hasClaude: claude !== "no",
+    isMax20: claude === "max20",
+    hasOpenAI: openai === "yes",
+    hasGemini: gemini === "yes",
+    hasCopilot: copilot === "yes",
+    hasOpencodeZen: opencodeZen === "yes",
+    hasZaiCodingPlan: zaiCodingPlan === "yes",
+    hasKimiForCoding: kimiForCoding === "yes",
+  }
+}