docs: refresh repository documentation

[lishaduck]

Summary

• remove generated starter docs, completed execution plans, obsolete briefs, and gitkeep placeholders
• update maintained architecture, operations, authentication, migration, and product documentation against current source
• remove the empty tools workspace and its references

Validation

• mise exec -- vp run fmt:check
• mise exec -- vp run --filter @petalnet/console-bus-rpc build
• mise exec -- vp run test (38 Console files / 264 tests; 2 adapter files / 122 tests)
• git diff --check
• all relative Markdown links resolve