Phase 2 of hyperhive#2196. The backend now pre-computes enrichment fields
on every SSE event (stream_enrich.rs); the frontend reads them directly
instead of running its own dispatch logic.
Removed (~330 lines of JS):
- fmtArgsGeneric / TOOL_ICONS / toolIcon / fmtRoom / fmtUser / fmtToolUse
renderStream changes:
- system events: dispatch on v._category (drop/thinking_tok/note/details)
+ v._summary / v._body instead of per-subtype if-chains; status tick
still overrides label client-side when stateName === 'compacting' since
elapsed time is a wall-clock value the backend cannot know at emit time
- tool_use: use c._category === 'rich' for rich-renderer routing,
c._icon / c._summary for flat rows
renderRichToolUse: toolIcon(name) -> c._icon (from backend enrichment)
stream_enrich.rs: also stamp _category: 'drop' on top-level
type=result / type=rate_limit_event so the frontend can use a single
_category check instead of separate type-based early returns
0f5367f948