Never-initialized variable type is not narrowed to undefined

### 🔎 Search Terms

narrow uninitialized, uninitialized undefined

### 🕗 Version & Regression Information

- This is the behavior in every version I tried, and I reviewed the FAQ for entries about `initialized`/`uninitialized`

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.9.0-dev.20250326#code/MYewdgzgLgBAZiEMC8MAUUDuIBcNoBOAlmAOYCUeAbiEQCYoB8MA3gFAwwBEArhAKb4oxYFC4BuDjCkB6GTH4QANiSgBaOkQgBDAEZL+asPwAe6lcZgABKAE8ADouDF76xRagySRdXX7AlbQJtKCJwCCkDWHB+PEISUhgAHxgeMD84En46SSkiOHQYlGRULBByVilOORgAPQB+KpgagDlEeykAXzZutgQQNC4ucnEgA

### 💻 Code

```ts
const foo = (two: string): void => {
"use strict";

// eslint-disable-next-line @typescript-eslint/init-declarations
let one: string | undefined;

if (one === two) {
// ^? let one: string | undefined
// Noop
}
}

foo("");
```

### 🙁 Actual behavior

The type is not narrowed, which prevents typescript-eslint from flagging this comparison that always fails: [typescript-eslint playground](https://typescript-eslint.io/play/#ts=5.7.2&fileType=.tsx&code=MYewdgzgLgBAZiEMC8MAUUDuIBcNoBOAlmAOYCUeAbiEQCYoB8MA3gFAwwBEArhAKb4oxYFC4BuDjCkB6GTH4QANiSgBaOkQgBDAEZL%2BasPwAe6lcZgABKAE8ADouDF76xRagySRdXX7AlbQJtKCJwCCkDWHB%2BPEISUhgAHxgeMD84En46SSkiOHQYlGRULBByVilOORgAOUR7KQBfNha2BBA0Li5ycSA&eslintrc=N4KABGBECmAeAu0B2ATAzpAXGA2uCU0aANgJZLyYCGxxkANPhJAA7ECuA5uZgALwBPFkQDGAJ1It4AWiJkKAehp18AXUbMx7YkSxhQEAL4hDQA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false)

### 🙂 Expected behavior

The `one === two` comparison should be flagged because it always returns false (there is no way `one` has any value other than `undefined`).

### Additional information about the issue

Also filed a related issue with ESLint: https://github.com/eslint/eslint/issues/19581

Reproduce the behavior using the TypeScript Playground link and the `one === two` example, then trace how control-flow narrowing handles a never-initialized variable. Compare the result with the expected always-false comparison and use the linked ESLint issue for related context. Done means the comparison is recognized as impossible without changing unrelated narrowing behavior.

Written by the indexing model from the issue text.