Expose cloud conversation storage setting in TUI

[warp-agent-staging]

Description

Expose agents.cloud_conversation_storage_enabled on all settings surfaces so it is included in the TUI settings schema and generated defaults. Runtime behavior and storage keys are unchanged.

Originating thread: https://warpdev.slack.com/archives/C0BDQDW8V5E/p1785420442437649

Linked Issue

APP-5065

Testing

• Testing-exempt category: constant-or-flag-default. The change only expands a declarative setting surface; a new test would tautologically assert the annotation, so the requester explicitly waived new tests.
• ./script/format --check
• cargo clippy commands from ./script/presubmit (passed)
• cargo nextest run -p warp -E 'test(/settings/)' (376 passed)
• cargo run -p warp --example generate_default_settings -- --surface tui /tmp/app-5065-tui-default-settings.toml (confirmed cloud_conversation_storage_enabled = true)
• cargo run -p warp --bin generate_settings_schema -- /tmp/app-5065-settings-schema.json (confirmed x-warp-surfaces: ["gui", "tui"])
• Full ./script/presubmit was also attempted; formatting and clippy/build passed, while the unscoped suite hit environment-dependent existing failures (build-cache permission behavior and integration tests requiring unavailable runtime services).

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

CHANGELOG-IMPROVEMENT: Make cloud conversation storage configurable in TUI settings.

Co-Authored-By: Oz oz-agent@warp.dev

[harryalbert]

• Expose cloud conversation storage setting in TUI #14533 👈 (View in Graphite)
• master

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