docs: specify the flow replay viewer

[osolmaz]

Summary

• add a dedicated flow replay viewer spec covering graph semantics, layout rules, replay controls, panel structure, and ACP session rendering
• link the viewer README to that spec and clarify that the full flow definition remains the main graph
• update the examples index to point at the new viewer spec

Validation

• pnpm run check:docs

[osolmaz]

Replay viewer implementation is now in place on this branch.

What changed:

• removed the redundant top chrome and duplicated status surfaces
• kept the full definition graph, but made start/end/branch semantics explicit in the node cards
• removed floating route-label pills from the graph and moved branch information into decision nodes
• made the ACP session the default inspector view and pushed secondary metadata behind compact disclosures
• tightened the sidebar, player, and panel spacing so the viewer reads like a dense inspection tool instead of a dashboard

Validation run on this head:

• pnpm run viewer:typecheck ✅
• pnpm run build:test && node --test dist-test/test/replay-viewer-view-model.test.js dist-test/test/replay-viewer-run-bundles.test.js ✅
• pnpm run viewer:build ✅
• pnpm run check ✅
• pnpm run check:docs ✅
• browser verification with agent-browser against http://127.0.0.1:4173/ using real saved PR-triage run bundles ✅

Browser checks verified:

• collapsible full-height left run rail
• compact one-line run rows
• no top navbar
• no floating white edge-label pills
• full definition graph with clearer semantics
• ACP session as the default readable pane with wrapped text and collapsed tool noise

One caveat: codex review --base main was attempted after pushing, but the local review tool stalled again on this machine after diff inspection and had to be interrupted. It did not surface any concrete P0/P1 finding before stalling.

[osolmaz]

Landed via temp rebase onto main.

• Gate: pnpm run check and pnpm run check:docs completed
• Land commit: eb95682
• Merge commit: 9348242

Thanks @osolmaz!