feat: add setting to expand thinking blocks by default

[bigstyle777]

Summary

Thinking blocks now appear as independent disclosures outside Process details, so users can read reasoning without opening tool output. They remain collapsed by default; General settings can expand them automatically and update already-mounted blocks immediately. Closes #411.

• Keep reasoning and contiguous process segments in their original order. A reply containing only thinking and a final answer no longer has an extra Process details wrapper.
• Preserve original session entry and block indices for deferred history loading, with cached requests and retry after a failed load.
• Persist the expansion preference in localStorage, with English, Simplified Chinese, and Traditional Chinese settings copy.
• Refine the shared settings switch with compact dimensions, theme colors, a subtle border, and keyboard focus, disabled, and busy states. Thinking disclosures expose their expanded state and show a matching chevron.

Validation

• TypeScript typecheck and ESLint pass.
• All 886 repository tests pass after merging the current main branch, including new checks for ordered thinking/process splitting and independent disclosure defaults.
• The repository end-to-end suite passes on desktop and mobile, covering bounded history, pagination, branch navigation, markdown, code, and tool calls.
• Playwright checks at 1280px and 390px cover default collapse, the actual settings switch and keyboard interaction, persistence after reload, live updates, interleaved tool calls, original deferred block indices, request caching and retry, unfinished turns, and search revealing the matched process segment. Light and dark screenshots were inspected.