CLI hangs/freezes when using `@filename:line` or `@filename:range` syntax

### What happened?

When attempting to reference a specific line or range of a file using the syntax `@filename:line` (e.g., `@app.js:10`) or `@filename:start-end` (e.g., `@app.js:10-20`), the CLI becomes unresponsive (hangs) and requires a force quit.

It seems the CLI might be trying to resolve the entire string (including the colon and numbers) as a file path, or it gets stuck in an infinite loop trying to parse the syntax.

**Steps to Reproduce:**
1. Start `gemini-cli`.
2. Type a prompt including a file reference with line numbers.
- Example: `Explain this function @src/main.js:15-25`, `@src/main.js#L10-#L25`, `@src/main.js:10` or `@src/main.js#L10`.
3. Press **Enter**.
4. The CLI freezes (cursor might blink, but no output or response occurs, and input is blocked).
5. `Ctrl+C` often fails to interrupt the process immediately.

### What did you expect to happen?

- **Ideal:** The CLI should read only the specified lines of the file, similar to other AI CLI tools (e.g., Claude Code).
I initially thought range reading was supported, but later realized it is not.
- **Fallback:** If this syntax is not supported, it should return a clear error message (e.g., "File not found" or "Line number syntax not supported") instead of hanging indefinitely.

### Client information

Client Information

Run `gemini` to enter the interactive CLI, then run the `/about` command.

```console
> /about
About Gemini CLI
CLI Version 0.29.5
Git Commit 2ef872e73
Model gemini-3-pro-preview
Sandbox no sandbox
OS darwin
Auth Method Logged in with Google
Tier Gemini Code Assist in Google One AI Pro
```

### Login information

Google Account

### Anything else we need to know?

I noticed this syntax (`@filename:line`) works seamlessly in other AI CLI tools (like Claude Code), which led to the confusion. If this feature is not supported in `gemini-cli`, a graceful failure with an informative error message would be much better than a freeze. This issue significantly disrupts the workflow as it forces a restart of the CLI session.

### Vedio

https://github.com/user-attachments/assets/1fb2d5ab-d16a-4020-9e2b-aa3644086a4f