test(ci): quarantine flaky macOS test_copy_prompt_from_input_honor_ps1_enabled

[BunsDev]

Description

What: Quarantines the flaky macOS integration test
shell_integration_tests::test_copy_prompt_from_input_honor_ps1_enabled in
.config/nextest.toml.

Why: It intermittently panics with No position for Copy prompt (a layout
step that finds no position for the "Copy prompt" affordance) on loaded macOS
runners — exhausting the default integration retries = 2 in a single run,
despite being unrelated to the code under test. It surfaced on the Run MacOS tests job for #209 (agent-panel/cli_chat changes that touch nothing in shell
integration/clipboard).

How: A macOS-scoped override isolates the test to a single-thread test-group
(copy-prompt-quarantine, reducing contention that starves layout) and raises
its retries to 4, mirroring the repo's existing settings-file-reload isolation
and update_manager platform-retry patterns. The override is temporary — to be
removed once the root cause is fixed.

Linked Issue

Closes #211 (tracks the root-cause investigation and eventual removal of the
override).

Testing

• .config/nextest.toml parses; override schema mirrors the existing
  update_manager (platform host cfg) + settings-file-reload (test-group)
  entries. ./script/check_ai_attribution + ./script/check_rebrand pass.
• Config-only; no code build. The override takes effect on the next macOS CI run.

Agent Mode

• CastCodes Agent Mode — PR via CastCodes. Join OpenCoven on Discord for support.

[Copilot]

Pull request overview

This PR mitigates flakiness in the macOS CI suite by quarantining the shell_integration_tests::test_copy_prompt_from_input_honor_ps1_enabled integration test in nextest configuration, reducing contention and increasing retries on macOS while the root cause is investigated (tracked by #211).

Changes:

• Added a dedicated nextest test-group (copy-prompt-quarantine) limited to max-threads = 1.
• Added a macOS-scoped profile.ci override to run the flaky test in that group and increase its retries to 4.
• Documented the rationale and linked the follow-up issue for eventual removal.

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