[FEATURE] Add /context --brief for token-efficient context checking

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The /context command consumes 4-5k tokens per invocation due to listing all MCP tools, agents, and skills. This is ironic for a command designed to monitor token usage.

Example from actual session:

Before first /context: Messages: 1.5k tokens (0.8%)
After first /context:  Messages: 10.4k tokens (5.2%)

What happened:

• User ran /context to check token usage
• Command output listed 85+ MCP tools, 60+ agents, 80+ skills
• This added ~4-5k tokens to conversation history
• Running /context again to verify consumed another ~4-5k tokens
• Total cost: ~10k tokens just to check token usage twice

The MCP tools, agents, and skills listings are rarely needed - users typically just want to know if they're approaching context limits.

Proposed Solution

Add a --brief flag (or make it the default) that shows only:

Context Usage
claude-sonnet-4-5-20250929 · 47k/200k tokens (24%)

⛁ System prompt:    3.0k (1.5%)
⛁ System tools:    22.3k (11.2%)
⛁ Custom agents:    4.7k (2.4%)
⛁ Memory files:     3.3k (1.6%)
⛁ Skills:           3.6k (1.8%)
⛁ Messages:        10.4k (5.2%)
⛶ Free space:       117k (58.3%)
⛝ Autocompact:     45.0k (22.5%)

Optional: Keep full output available via /context --full for when users need detailed listings.

Impact

This would reduce context checking from ~4-5k tokens to ~50-100 tokens, making it practical to check context usage without ironically consuming massive context.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

_No response_

Additional Context

_No response_