perf(web): router updates no longer re-render thread route consumers - #20837

Eligibility
This is a contained web performance refactor that replaces allocation-heavy route selectors with stable primitive parameter selections across the chat layout and related consumers. Route changes still propagate normally, while unrelated router updates stop triggering these renders; no schema, deployment, security, billing, default, or static-analysis behavior is changed.

Notes:
No code owners found in target merge base efdaa4b