Refresh stale component READMEs against verified runtime facts

Fix component README statements that contradict the code, found while writing the KNOWLEDGE.md coverage (BA-7303).

Verified stale points: agent/README.md claims RPC port 6011 (actual 6001) and mischaracterizes the watcher direction as Agent-to-Manager HTTP; storage/README.md describes a directory tree that no longer exists (vfs/ top level, services/vfolder.py) and a generic per-folder quota story instead of the quota-scope model with CAP_QUOTA; appproxy READMEs claim gRPC support (REST only), stale ports (6120/6130/6030/6040/5050 vs actual 10200/10201/10205-10300), a coordinator-to-worker health probe (actual: worker-to-coordinator ping), and etcd circuit paths (circuits live in the coordinator DB and travel over the event bus); common/events/README.md claims DLQ support and retry backoff that do not exist (retries are capped then dropped, no DLQ).

The corresponding KNOWLEDGE.md documents carry the correct facts; this issue aligns the human-facing READMEs with them.

JIRA Issue: BA-7306

Start with the corresponding KNOWLEDGE.md entries, then compare agent/README.md, storage/README.md, the appproxy READMEs, and common/events/README.md against the verified runtime facts in the issue. Update each stale statement about ports, request direction, quota scope, protocol support, circuit storage, and retry behavior; done means the component READMEs no longer contradict those documented facts.

Written by the indexing model from the issue text.