Add Cursor Agent to the default picker and usage panel

[shawnyeager]

Adds Cursor Agent to Setup → Defaults → Agent and to the agents usage panel.

If cursor-agent is already on PATH, selecting Cursor writes the default and launches it (--yolo --trust). If it is missing, Omarchy fetches Cursor's official Linux tarball from downloads.cursor.com and installs it as cursor-agent, not agent. No mise registry entry. No third-party asdf plugin.

The agents panel collects Included / Cursor Models / Other Models from Cursor's dashboard APIs (GetCurrentPeriodUsage, paged GetFilteredUsageEvents, GetAggregatedUsageEvents). Credentials come from the IDE state.vscdb or ~/.config/cursor/auth.json.

Menu and panel marks use Cursor's 2D cube from https://cursor.com/brand (U+E90A in the Omarchy icon font). The same glyph replaces the generic file icon on Defaults → Editor → Cursor and Install → Editor → Cursor.

Related work

This is the same feature as several open PRs. It combines them and is meant to land instead of opening another parallel slice:

• Supersedes Add Cursor Agent as a default coding agent #6969 (picker + official tarball install + thinner collector). That review dropped the asdf plugin; this keeps that install path.
• Supersedes Add Cursor usage collector to the agents panel #7087 (usage collector and shared-reset LIMITS header). This uses that collector, with textFormat: Text.PlainText on the new countdown so qml-text-format-test passes.
• Supersedes Add Cursor to the default coding agent picker #8450 (picker via mise). Cursor still has no mise registry entry.
• Supersedes Add Cursor CLI as a default coding agent #6827 (picker, plus editor wiring this PR does not take).
• Related: Add Cursor agent usage collector #6604 (Cursor usage collector, also adds Grok usage). This PR is Cursor-only.

What is different from #6969

• Collector is Add Cursor usage collector to the agents panel #7087's: pages usage events, reads IDE state.vscdb as well as CLI auth.json.
• Glyph is Cursor's official 2D cube, not Simple Icons, and it is used on the editor/install rows too.
• omarchy-install-cursor-agent uses omarchy-cmd-missing / type -P so bin-style-test passes.
• Rebased on current quattro.

Test plan

• OMARCHY_PATH=$PWD bash test/shell.d/default-agent-test.sh
• OMARCHY_PATH=$PWD bash test/shell.d/install-cursor-agent-test.sh
• OMARCHY_PATH=$PWD bash test/shell.d/agent-usage-cursor-scanner-test.sh
• OMARCHY_PATH=$PWD bash test/shell.d/menu-test.sh
• OMARCHY_PATH=$PWD bash test/shell.d/bin-style-test.sh
• OMARCHY_PATH=$PWD bash test/shell.d/qml-text-format-test.sh
• Open Setup → Defaults → Agent and confirm Cursor appears with the cube glyph
• With cursor-agent already on PATH, select Cursor and confirm it launches with --yolo --trust
• With it missing, confirm the official tarball is installed as cursor-agent
• With Cursor signed in, run omarchy agent usage update cursor and confirm the agents panel Cursor tab