perf(flow-chat): smooth large history session rendering

[limityan]

Summary

• Render completed historical model-round groups progressively: first 80 groups, then 80 more every 16ms; streaming rounds stay fully rendered and already-rendered rounds do not shrink when streaming completes.
• Fix restored TodoWrite duplicate React keys when legacy/truncated todo ids collide.
• Replace internal session-view truncation markers with user-facing preview text across restored tool cards and copy/export paths.
• Fix the usage-report Tooltip ref warning by making the file label ref-forwarding.

Performance / Diagnostic Data

• Problem logs showed large historical session opens producing 156 and 263 duplicate-key warnings keyed by [truncated for session view]; the stack traced to TodoWriteDisplay.
• Initial render work for completed historical rounds is now bounded from N groups to 80 groups on the first render, with the rest appended in 80-group chunks. For a 263-group class of case, first-render group work is capped at 80 instead of 263, a 69.6% reduction in initial group render volume.
• Local debug logs after the duplicate-key/truncation-path fixes showed duplicate-key warnings reduced to 0 and legacy truncation marker logs reduced to 0. This PR also fixes the remaining usage-card ref warning with focused test coverage.
• This PR does not claim cold-start or interactive_shell_ready improvement; perf(startup): continue reducing desktop startup and interactive shell readiness time #949 remains open for that follow-up optimization.

Risks

• Very large historical sessions reveal older groups progressively instead of all in one synchronous render. The history loader is visible while this happens; copy/export still reads from the full session state rather than only visible groups.
• The session preview compaction marker text changes from an internal placeholder to user-facing preview text. The compaction behavior itself is unchanged.

Verification

• pnpm run lint:web
• pnpm run type-check:web
• pnpm --dir src/web-ui run test:run
• cargo check -p bitfun-desktop
• cargo test -p bitfun-desktop
• git diff --cached --check

Refs #949