New 'max effort' mode with a status-line reminder

What

• A new "max effort" mode was added: a helper decides when to force maximum effort, gated by a reminder-enabled check before it's applied.
• A status-line reminder ("Max effort · … · /effort to change") is shown when effort is set to max; whether it appears is controlled by the CLAUDE_CODE_MAX_EFFORT_REMINDER environment variable, falling back to a remote flag (tengu_proud_clover, off by default unless enabled server-side).
• The VS Code extension's feature-gate table gained the corresponding max-effort reminder gate, wired from maxEffortReminderEnabled.
• The reminder is shown in a warning color rather than a subtle one when the environment variable or flag is set.
• Underneath, the request-building code for side-queries now accepts an effort option that becomes output_config.effort on the API call; if a model rejects it, Claude Code remembers the model doesn't support it and retries without the field, logging a telemetry event.

Why

This lets you run Claude Code at maximum effort and know at a glance when that mode is active, via /effort to change it, while the underlying request logic gracefully falls back for models that don't support the effort parameter.