[FEATURE] /context in the classic renderer should default to the compact summary, with /context all for the full listing

### Preflight Checklist

- [x] I have searched existing issues and this is not a duplicate
- [x] I have confirmed this is a feature request for Claude Code

### Problem Statement

In the classic renderer, plain `/context` still prints the full per-item listing of MCP tools, custom agents, memory files, and skills. The question the command exists to answer is "how full is my context window, and where is the pressure?" That answer sits under a long listing that the user did not ask for.

In #64996, a maintainer (@bcherny, 2026-08-17) confirmed the remaining scope:

> Outside fullscreen mode the default is still the full listing, so leaving this open for the compact-by-default part.

The stale bot closed #64996 on 2026-09-15 with no further maintainer action. The bot's closing note asks for a new issue when the topic is still relevant, so this is that issue. The CHANGELOG through v2.1.273 lists no change to the classic `/context` default.

### Proposed Solution

Make the classic renderer match the fullscreen renderer:

- `/context` shows the usage graph and the category summary, with the per-item listings collapsed to one-line summaries.
- `/context all` shows the full listing, as it does today.

The fullscreen renderer already has this behavior, so the change is a parity fix, not a new design.

### Alternative Solutions

A `contextVerbose` setting or a `/context brief` subcommand. Both add surface area for a default that fullscreen already made.

### Priority

Medium - Would be very helpful

### Feature Category

Interactive mode (TUI)

### Use Case Example

A user on the classic renderer runs `/context` several times in a long session to watch the window fill. Each run scrolls pages of tool and skill names past the one number they wanted. The per-item detail is already reachable through `/mcp`, `/agents`, `/memory`, and `/skills`.

### Additional Context

Prior filings on the same request, all closed by automation before the classic default changed:

| Issue | Ask | Outcome |
| --- | --- | --- |
| #18056 | `/context --brief` | closed |
| #19595 | `/context -m` flag | closed |
| #27592 | `/context --compact` | closed |
| #48798 | `/context` is too verbose | closed |
| #64996 | `/context` compact by default, `/context all` for full | stale bot, 2026-09-15 |

The classic renderer is still the default for anyone who first used Claude Code before May 6, 2026 and has no saved `tui` setting, per the fullscreen docs. This gap affects the long-time user base.

Start at the /context command entry point and compare how the classic and fullscreen renderers choose their default output. Verify that plain /context uses the compact summary while /context all preserves the full listing, then exercise both modes in the classic renderer to confirm the behavior.

Written by the indexing model from the issue text.