docs: fix stale file references and statuses

[MasamiYui]

Summary

Four places in the current (non-archive) documentation point at things that no longer exist or describe a status that is no longer true:

• SECURITY.md §2 and §4 cited apps/desktop/src/main/__tests__/web-search-boundary.test.ts and claude-subscription-ipc-boundary.test.ts as the contract tests for the main→renderer token boundary. Both were deleted in test: improve test suite signal quality #1851. The section now names the tests that enforce it today: settings-ipc-helpers.test.ts (Tavily and bot credentials) and runtime-host-connections-ipc-main.test.ts (Connection credentials, including OAuth subscriptions and custom headers).
• ARCHITECTURE.md reading paths described the Desktop conversation projection as "proposed … not yet implemented", while the linked docs/architecture/desktop-conversation-host-projection.zh-CN.md opens with 状态：已实施. Wording updated to match.
• ARCHITECTURE.zh-CN.md was missing that reading-path entry entirely (the one Chinese-only document was absent from the Chinese index). Added, keeping the two editions in step.
• docs/tui-live-ctx-updates.md still read Status: design after feat(cli): refresh the statusline ctx segment per settled provider request (#4545) #4550 shipped packages/cli/src/tui-context-refresh.ts and wired it into pi-tui-runner.ts; it also referenced session-trace-refresh.ts at its pre-move path. Status now says implemented and the path points at features/workbar/tools/inspector/.

No code changes.

Verification

• Relative-link check across all 190 Markdown files in the repository (excluding node_modules, dist, website): 469 links, 0 broken, before and after
• Every backticked source path in SECURITY.md, ARCHITECTURE*.md, and docs/tui-live-ctx-updates.md now resolves to an existing file
• Confirmed with git log that tui-context-refresh.ts landed in f4aae2a (feat(cli): refresh the statusline ctx segment per settled provider request (#4545) #4550) and that the two SECURITY.md test files were removed in 4e29c2e (test: improve test suite signal quality #1851)
• ARCHITECTURE.md and ARCHITECTURE.zh-CN.md now carry the same set of reading-path links

AI use

Select exactly one:

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Claude Code — scanned the docs for stale paths/statuses, verified each against git log and the current tree, and drafted the edits. Commit carries a Generated-by: Claude Code trailer.

Checklist

• Tests cover the change and fail without it — not applicable (documentation only)
• Lint, format, typecheck and the affected suites pass locally — no source files touched; link check clean

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No