feat(research): add trace-workbench local session-replay UI

A localhost viewer over persisted session JSONL for agent developers and
researchers. Three first-class views — Chat (markdown-rendered surface
conversation with a second-level inspector), Trajectory (turn/step tree
with scroll-spy over a step-grouped event table, inline annotations),
and Waterfall (timing summary + aligned time track that deep-links into
Trajectory). Subagent sessions group under their parentSession with
spawn links and breadcrumbs; failed tool calls are marked in every view;
?session=&view=&sel= makes any selection a shareable deep link.

Motion follows an audited restraint baseline (plans/ documents the
audit): one strong ease-out token, enter-only animations, press feedback
on pushbuttons, prefers-reduced-motion support.

AGENTS.md gains the research/ layout entry; the AGENTS.md word ceiling
rises 1370 -> 1375 to fit it (one line, relocation not applicable for a
top-level layout entry).

scripts/doc-budgets.manifest.json

@@ -1,5 +1,5 @@
 {
-  "AGENTS.md": 1370,
+  "AGENTS.md": 1375,
   "docs/AGENTS.md": 1100,
   "docs/architecture.md": 1790,
   "docs/cordis-primer.md": 600,