[FEATURE] settings.json key to fully disable IDE selection/open-file context injection

### Preflight Checklist

- [x] I have searched [existing requests](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20label%3Aenhancement) and this feature hasn't been requested yet
- [x] This is a single feature request (not multiple features)

### Problem Statement

## What I want

A `settings.json` key that turns off IDE context injection completely and permanently — something like `"ideContext": "off"`.

Set once, never think about it again. No file path, no selection, no chip in the input box. `/ide` stays connected so I keep diffs in the IDE viewer, clickable `file:line`, and `getDiagnostics`.

## Why

With the JetBrains plugin connected, every prompt I send carries the active editor file. Per the docs: "While connected, the CLI includes your current editor selection and the path of the active file as context on each prompt you send."

I do not want that. Most of my prompts are about a migration, a DB query, a branch, a review — whichever tab happens to have focus is noise, and it gets fed to Claude regardless. On top of that the indicator sits inline with the input and indents **every** line of a multi-line prompt by its own length; with the panel docked to the right of the IDE, a long PHP filename eats roughly half the remaining width, per line.

## Why the existing workarounds don't work

The docs offer exactly one: a `Read` deny rule per path. That blocks reading the file too, so I lose real functionality to silence a UI feature. The only other exit is `/ide`, which disconnects the whole integration — diffs, `file:line`, diagnostics, all of it.

So today the choice is: keep an unwanted attachment on every prompt, or give up features I actually use. There is no third option, and the JetBrains docs page documents none.

## Environment

- Claude Code 2.1.274, Windows 10 Pro 19045
- PhpStorm + Claude Code JetBrains plugin, panel docked right, `"tui": "fullscreen"`

## Related

- #94191 — asks for a *runtime* toggle and for moving the indicator to the status bar, explicitly stating "hiding it is not the goal". My ask is the opposite: a persistent off switch, no indicator, no attachment.
- #94908 — same "add a setting to disable it" request, but for selection attachment in terminal mode.
- #94189, #94217 — the indicator also never clears after the file/tab is closed.

Blunt version: this crap pisses me off, and it is the one thing making the JetBrains integration a net negative for me.

### Proposed Solution

### Alternative Solutions

_No response_

### Priority

High - Significant impact on productivity

### Feature Category

Interactive mode (TUI)

### Use Case Example

_No response_

### Additional Context

_No response_

Start by tracing settings.json handling and the /ide integration path that injects the active file, selection, and input indicator. Reproduce with the JetBrains plugin connected, then verify that a persistent off setting removes the attachment and indicator while preserving diffs, file:line links, and getDiagnostics.

Written by the indexing model from the issue text.