fix(tui): avoid repeated history reads during streaming

[kingsword09]

Streaming session events could schedule a full conversation read every 80 ms, even when only text changed. Filter presentation-only events in the persistent subscription and reuse a compact token/cache summary during activity polling.

Completed requests, changed usage, prompt results and history changes invalidate the summary. Session switches discard it, and late reads cannot overwrite a newer revision. The cache retains statistics rather than message bodies or tool output.

Validation:

• bun run typecheck
• bun run sync:locked with Desktop 3.14.3
• bun run test:unit (657 passed)
• bun run test:tui, including a real-PTY regression for streaming, tool progress, completion and resume
• bun scripts/check-runtime.ts
• bun run check:tui
• git diff --check

[pkg-pr-new]

npx https://pkg.pr.new/zcode-app-cli@a6667b4

commit: a6667b4