[Repo Assist] chore: add rust-version, repository, homepage, and readme to Cargo.toml

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🤖 This PR was created by Repo Assist, an automated AI assistant.

What

Adds four standard fields to the [package] section of Cargo.toml:

rust-version = "1.86"
homepage     = "https://github.com/shanselman/winget-tui"
repository   = "https://github.com/shanselman/winget-tui"
readme       = "README.md"
```

No code changes.

## Why

### `rust-version`

`ratatui 0.30` — the most constrained direct dependency — declares `rust-version = "1.86.0"`. Without a matching declaration in this crate, `cargo` will silently attempt to compile on older toolchains and fail with a confusing dependency error rather than a clear MSRV message. Declaring `rust-version = "1.86"` gives users and CI a fast, clear failure if the toolchain is too old.

### `repository` / `homepage`

These are standard Cargo metadata fields used by:
- **deps.rs** and **lib.rs** to link back to the source
- **cargo doc** to generate a source link in the documentation
- Any future crates.io publish

Both point to the GitHub repo, consistent with what users would expect.

### `readme`

Points `cargo doc` and crates.io tooling at the existing `README.md`. Without it, documentation-generation tools may not pick up the project description.

## Test Status

```
cargo check --all-targets  → clean
cargo fmt -- --check       → clean
cargo clippy -- -D warnings → clean
cargo test                 → 231 passed (unchanged — no code changes)

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