feat(web): surface frontend tool call activity - #418

Summary

• render frontend tool-call activity emitted by the realtime gateway
• keep tool activity in chronological order with assistant messages
• add focused client and component coverage for tool-call lifecycle states

The presentation model keeps only bounded, non-content metadata: call id, surface
(frontend / backend), tool name, status, timestamps/duration and an optional
error code. Raw arguments and results are deliberately dropped, the retained call
list is capped at 64, and terminal states cannot be reverted by a late event.

Scope is web presentation plus the two protocol/contract docs lines that describe
tool.call as a presentation-only event. No Gateway, backend or client-state
behaviour is changed.

Update — rebased onto current main

The branch had drifted 8 days behind main (385 files changed since the merge
base), so it was rebased onto main and force-pushed. Two things worth calling
out:

• Conflicts were limited to CHANGELOG.md (kept both entries, new entry on top)
  and .github/workflows/ci.yml. Both are resolved; the final diff is
  +550 / −13 across 12 files.
• The Windows npm test retry commit that had been stacked on this branch was
  dropped. That change was declined on its own merits in ci: retry Windows suite on silent test-process exits #422/ci: preserve Windows test crash diagnostics #442, so it does
  not belong in this PR's scope. ci.yml is now untouched by this branch.

Validation

Re-run locally on this rebased head (Windows, Node 24.11.0):

• npm run test --workspace web — 158 passed, 0 failed
• npm run build — succeeded
• node --test server/test/realtime-gateway.test.mjs — 5 passed, 0 failed
• npx eslint . — clean

Closes #230
Closes #231