fix(web): show the context window meter by default and keep it a normal setting

[kratofl]

What Changed

The composer's context window indicator is visible again by default. Its toggle moved out of Legacy features into Settings → General, next to the other composer options, with a reset button like its neighbours. Settings search finds it as "Context window indicator" without the legacy suffix.

The contextWindowMeterEnabled client setting stays. It now decodes to true when absent, so existing users get the meter back without touching anything, and anyone who explicitly switched it off keeps it off. The composer gating and slot reservation logic are unchanged.

Why

#9190 hid the indicator behind a default-off legacy toggle with no stated reason. Users read the "legacy" label as a deprecation notice. That PR's thread and #9352 collect a lot of requests to bring it back. Seeing current context occupancy is how people decide when to compact or start a fresh thread, and it is the same number Claude Code and Codex show in their own status lines.

Keeping it optional is reasonable for anyone who wants a cleaner composer, so this keeps the switch but makes it a normal, supported setting.

Closes #9352

UI Changes

Before/after screenshots follow shortly.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes (not applicable, no motion)

Built by Claude Fable 5.1 in T3 Code through the Claude Code harness.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Context window indicator is now enabled by default, showing usage information such as tokens, percentages, and remaining capacity.
  • The indicator can still be disabled in settings.
  • Context window indicator settings are now available under Behavior rather than Legacy features.
  • Settings search now lists the indicator as a current feature with updated search terms.

• Bug Fixes

  • Updated default-setting restoration and search behavior to reflect the indicator’s current status.

[kratofl]

Closing in favor of #12095, which was opened first and makes the same move out of Legacy features. The only difference here was defaulting the meter to on, which most of the #9352 thread asked for. That is better raised on #12095 than as a competing PR.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — The PR changes the context-window meter from an opt-in to an enabled-by-default product behavior, affecting the existing composer path while preserving explicit opt-outs. It also relocates the setting into General, so the default change warrants human review.

Notes:

• Code review disabled. Approvability was decided on eligibility alone.

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