feat(webui): expand and organize settings with autosave

[chengyongru]

Settings currently leave many non-channel options editable only in config.json. This exposes 41 configuration fields through validated settings endpoints and organizes common controls on their feature pages, with low-frequency settings in Advanced.

• Use the existing visual style with shared responsive alignment, consistent controls, dependent-field disclosure, and compact save feedback.
• Automatically save ordinary edits. Keep explicit saving for listener changes, and show the existing restart-required workflow for newly exposed runtime settings.
• Keep Memory settings to one memory-consolidation switch, mapped directly to agents.defaults.dream.enabled. Other memory parameters remain in config.json; existing memory reading and session compaction are unchanged.

Backend scope is limited to settings payloads, validation, persistence, and route registration. This PR does not change AgentLoop, cron scheduling, session management, workspace switching, or listener lifecycle. Saving does not introduce live reload or automatic service restarts.

Validation:

• 55 focused backend settings tests passed, including assertions that saving neither calls runtime refresh nor restarts the API service.
• Rebased onto main at 92a297a without conflicts; range-diff confirmed the existing commits were unchanged. All 97 settings UI tests and 55 focused backend tests passed after rebase. Removing the default workspace control subsequently passed 12 UI and 31 backend tests.
• WebUI build, ESLint, Ruff, basedpyright, and whitespace checks passed.
• Isolated browser verification confirmed the single Memory switch saves and persists across refresh, retains a restart notice, and leaves the running Dream schedule unchanged. Verification processes and ports were cleaned up.

Draft follow-up:

• A visible compatibility message now replaces a blank Memory page when the backend omits the new settings payload. The originally reported development frontend/backend version mismatch still needs confirmation on that setup.