[codex-rs] Add writes app approval mode

[zamoshchin-openai]

Summary

• Adds writes to AppToolApproval and exposes it through config and app-server schemas, including [apps._default].default_tools_approval_mode.
• In writes, tools with readOnlyHint = true skip approval; all other tools prompt, including non-destructive writes and tools without annotations.
• Prevents session or persistent approval choices in this mode so later writes still prompt.

Why

auto only prompts for risk-hinted actions, while prompt also interrupts reads. Apps need a middle mode that gates writes without prompting for declared read-only actions.

Validation

• just write-config-schema
• just write-app-server-schema
• just fmt
• just test -p codex-core mcp_turn_metadata (4 passed)
• just test -p codex-core writes_mode (2 passed)
• just test -p codex-app-server config_read_includes_apps (1 passed)
• just test -p codex-app-server-protocol (251 passed)
• just test -p codex-config (200 passed)
• just test -p codex-cli (300 passed)
• just fix -p codex-core -p codex-config -p codex-app-server-protocol -p codex-app-server -p codex-cli