fix(cursor): support ACP parameterized model picker

[swear01]

Closes #968

Summary

• advertise Cursor ACP parameterized model picker support during initialize
• synthesize Cursor fast variants from separate model + fast config options for the existing picker/catalog path
• apply Cursor CLI SKUs through ACP config patches so composer-2.5 sets fast=false and composer-2.5-fast sets fast=true
• restore the in-session Cursor Variant selector in HappyComposer

Test plan

• cd cli && bunx vitest run src/cursor/utils/cursorModeConfig.test.ts src/cursor/utils/cursorAcpModelsSnapshot.test.ts src/agent/backends/acp/AcpSdkBackend.initialize.test.ts src/agent/backends/acp/AcpSdkBackend.test.ts
• bun typecheck
• bun run test
• manual ACP smoke: runCursorAcpModelProbe returns both composer-2.5[fast=false] and composer-2.5[fast=true]
• manual ACP smoke: applying composer-2.5 returns ACP config option fast.currentValue = "false"; applying composer-2.5-fast returns fast.currentValue = "true"

[github-actions]

Findings

• No issues found with confidence >= 80% in the added/modified lines.

Summary

• Review mode: initial
• Reviewed the Cursor ACP parameterized model picker changes across CLI snapshot/application paths and the restored web variant selector. Residual risk: behavior still depends on Cursor's live ACP configOptions shape for model + fast beyond the covered fixtures.

Testing

• Not run (automation)

HAPI Bot