Fix Cursor always selecting fast mode

[georgecollier-nqu]

Problem

Cursor supports a parameterized ACP model picker, but bb does not advertise its capability. Cursor therefore enters compatibility mode and returns combined variant IDs instead of separate model settings.

This has three user-visible consequences:

• The bb model catalog can miss Grok reasoning levels. High effort then falls back to the model default.
• The default service tier cannot disable a stored Cursor Fast mode preference. Requests can use Fast mode when the toggle is off.
• bb mixes Cursor CLI model IDs with ACP session model IDs. These IDs do not have the same selection contract.

Fix

This change advertises _meta.parameterizedModelPicker for Cursor model discovery and live sessions. Cursor then returns bare model IDs plus effort and fast config options.

The bridge now:

• selects the bare ACP model ID;
• maps reasoning levels to the effort config option;
• maps default to fast=false and fast to fast=true;
• probes Grok models first within the bounded catalog discovery time;
• bumps the host daemon protocol version for the changed session payload.

Testing

• Passed focused agent runtime, provider catalog, and daemon contract tests.
• Passed affected package typechecks.
• Verified eight real Cursor sessions: Grok 4.5 and 4.6, medium and high effort, with default and Fast mode.
• Confirmed Cursor persisted the expected model variant for every case.

This change is separate from #1612, which tracks recursive workflow tool schemas.

AGENT GENERATED: by GPT-5.6 Sol