CLI: /feedback command accessible when feedback_enabled is false

Summary

When feedback_enabled is set to false in configuration, the /feedback slash command remains visible in the command list and executable. It shows a dismissable popup rather than being fully blocked. For deployments that need all non-essential traffic disabled (especially session log uploads), the command should be completely inaccessible.

Environment

• Component: codex-rs CLI/TUI
• Files involved:
• codex-rs/tui/src/chatwidget/slash_dispatch.rs (lines 150-161)
• codex-rs/tui/src/slash_command.rs (is_visible method, line 230)
• codex-rs/tui/src/bottom_pane/feedback_view.rs (feedback_disabled_params, line 437)

Steps to Reproduce

1. Set feedback_enabled = false in configuration
2. Launch the Codex TUI
3. Type / to see available commands — /feedback is listed
4. Run /feedback — a dismissable popup is shown instead of being rejected

Expected Behavior

When feedback_enabled = false:

• /feedback should not appear in the slash command list
• If typed directly, it should be rejected with a clear message (similar to how other gated commands like /goal check their feature flag)
• No feedback-related UI flow should be reachable

Actual Behavior

• /feedback appears in the command list regardless of the flag
• Running it shows a "Sending feedback is disabled" popup with a Close button
• The is_visible() method in slash_command.rs does not consult feedback_enabled
• While the backend (feedback_processor.rs:45) does reject the actual upload, the TUI-side gate is insufficient — it still enters the feedback UI flow

Why This Matters

The /feedback flow uploads session logs to external servers. For environments where non-essential outbound traffic must be fully disabled, a dismissable popup is not a sufficient gate. The command should be completely hidden and rejected when the configuration says it's disabled.

Suggested Fix

1. Add a feedback_enabled field to BuiltinCommandFlags and filter /feedback from the command list when false
2. In is_visible() or the command filtering logic, hide the command when the flag is false
3. Keep the backend rejection in feedback_processor.rs as a defense-in-depth measure