feat(web): Code Mode sub-calls in the trajectory and waterfall views

Trajectory: the layout fold interleaves one subtool cell per sub-dispatch
after its parent Tool cell (assistant-block calls, orphan results, and
running calls alike), indexes sequential across the interleave; settled
durations come from the start/settle pair, running sub-calls show the
em dash. New Sub tag (business tint) + 28px indent.

Waterfall: deriveSubSpans folds the dispatch index into per-turn lanes
with REAL wall time — each parent's window is first start → last settle
and every lane's offset/width is its fraction of it, so parallel
sub-calls visibly overlap; running lanes extend to the window end at
reduced opacity. Lanes draw under the owning turn row.

Both views read codeDispatches through the standard snapshot hook; no
new wire data, replay renders identically to live. Specs pin interleave
order, durations, the running arms, window fractions, and the rendered
lane.

.agents/notes/implemented/feature/2026-07-26-code-mode-trajectory-waterfall-spans.i18n.yaml

@@ -0,0 +1,6 @@
+# Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
+# side as of the last confirmed-consistent state. Both languages carry equal authority;
+# after editing either side, bring the other along and re-record with:
+#   pnpm run verify-translation-pairing --write
+2026-07-26-code-mode-trajectory-waterfall-spans.md: 54449bcf8612a39461a769173d7f60c742f67ad8
+2026-07-26-code-mode-trajectory-waterfall-spans.zh.md: fbfb26c3a62554d60a6cb561ead78e10cd4115cd