docs(coordination): architecture-review kickoff prompts + followup planning

Adds the four kickoff prompts that drove the 2026-05-04 whole-codebase
architecture audit (PM + DEV-A/B/C reviewers), the planning prompt
that converts the synthesis into three implementation plans, and the
PM + DEV-A/B/C kickoff prompts for executing those plans in parallel.

Also updates the existing v0.5.1-* prompts with the relay-server
fallback section that references the new tools/relay/call.py shim.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/superpowers/coordination/v0.5.1-dev-b-prompt.md

@@ -83,8 +83,22 @@ export function teardownSecuritySection(): void;
 - Device sections read/write `chrome.storage.local`. Vault sections call `sendMessage` to the service worker.
 - Don't merge to main. The PM owns merges.
 
+## Relay server
+
+A message-bus MCP server is running on `localhost:7331`. You have three native tools:
+
+- `post_message(from, to, kind, body)` — push a message; your `from` is always `"dev-b"`
+- `read_messages(for)` — drain your inbox; call with `for="dev-b"` before each task
+- `list_pending(for)` — check inbox count without consuming
+
+Recipients: `pm`, `dev-a`, `dev-b`, `dev-c`. Use these instead of asking the user to copy-paste. Before starting each task: `read_messages(for="dev-b")`. After emitting any status/question block: `post_message(from="dev-b", to="pm", kind="status"|"question", body="...")`.
+
 ## Coordination protocol
 
+Before starting each task, call `read_messages(for="dev-b")` to drain your inbox.
+
+When posting a status update, call `post_message(from="dev-b", to="pm", kind="status", body="...")` with the body:
+
 ```
 ## STATUS UPDATE — DEV-B
 Time: <iso8601>
@@ -1064,6 +1078,8 @@ gh pr create --title "feat: settings UX redesign — left-nav sectioned layout (
 
 - [ ] **Step 6: Post status to PM**
 
+Call `post_message(from="dev-b", to="pm", kind="status", body="...")` with:
+
 ```
 ## STATUS UPDATE — DEV-B
 Time: <iso8601>