[codex] Clean up experimental feature popup backend wiring

[canvrno-oai]

This is a small code cleanup that moves the TUI experimental-features popup onto the app-server surfaces that already expose feature metadata and enablement. The popup now loads feature rows from experimentalFeature/list and persists remote-session toggles through the app-server config API, keeping local and remote behavior aligned. It also tightens the save path so only changed rows are written back to config.

Changes

• Load experimental feature metadata and effective enablement from experimentalFeature/list.
• Preserve cwd/profile context for list requests and remote config writes.
• Avoid persisting runtime-only enablement by dirty-tracking popup rows.
• Add quoted key-path segment handling so dotted profile names save to the intended profile.
• Regenerate app-server protocol schemas for the new list parameters.

Testing

• just fmt
• cargo test -p codex-app-server write_value_preserves_comments_and_order
• cargo test -p codex-app-server
• cargo test -p codex-tui app_server_session::tests