docs: reorganize navigation and clarify runtime guides

[seratch]

This pull request updates the documentation IA and core guides so it is easier to find the right entry point for first runs, orchestration, streaming, and conversation state.

• Reorganize the docs navigation across locales so foundational guides appear earlier, related topics are grouped more clearly, and localized API reference sections are exposed consistently.
• Refocus the quickstart on the first successful agent run, then layer in tools and handoffs with clearer examples and links to matching repo examples.
• Clarify how to choose between result.to_input_list(), sessions, conversation_id, and previous_response_id, including how streaming completion, approvals, resume flows, and compaction interact with those choices.
• Tighten terminology around agent orchestration and local/runtime execution tools, and update translation mappings plus localized headings so the English rename stays aligned in Japanese, Korean, and Chinese docs.