docs(a2a): add verified v2.6 controller-worker evidence

[tonkevip]

Summary

• Consolidates the Hermes ↔ OpenClaw A2A v2.6 controller/worker verification into this single clean PR branch.
• Removes unrelated local upgrade/runtime backup changes from the previous branch contents.
• Keeps only A2A v2.6 docs, validators/runners, mock/dry-run artifacts, and the final passing live evidence directory.
• Documents the OpenClaw gateway blocking-response root cause and runtime patch used for final live validation.

Verified final live evidence

• examples/v2.6.0/live-final-fix2-20260530T135309Z
• ok=true
• receipt_count=2
• accepted_count=2
• overall=accepted_with_boundary
• evidence validator passed

Redaction / safety

• Exact clean PR path set scanned before branch update.
• Secret/header literal hits: 0.
• No Authorization: literal, no Bearer <token> literal, no token_recorded=true, no credential_recorded=true in the clean PR path set.

Boundary

• This PR records Hermes-side A2A evidence and runbooks.
• The OpenClaw gateway runtime fix was applied on the live OpenClaw host for validation and should be upstreamed separately to win4r/openclaw-a2a-gateway for long-term persistence.

[alt-glitch]

⚠️ This PR is titled as docs-only but modifies core production files: agent/conversation_loop.py, gateway/run.py, gateway/stream_consumer.py, gateway/platforms/base.py, hermes_cli/goals.py, hermes_cli/kanban_db.py, plugins/image_gen/, tools/approval.py. Also includes .bak files (gateway/platforms/feishu.py.bak*). Needs careful review — the scope far exceeds A2A documentation.

[teknium1]

Closing in favor of #41711, which consolidates the entire A2A protocol cluster into a single platform-adapter plugin with zero core edits.

This pr contributed this controller-worker evidence PR. The A2A protocol work is being consolidated into a single plugin; this 72-file docs/evidence PR doesn't fit that shape. Thanks @tonkevip!

See #41711 — the PR body has a table tracing each requirement back to its source issue/PR.