docs(readme): update assistant roster, prompt layers, repo structure

- Update assistant lists (added Shawn, Watson, David, CASE, AWS SA; modified Scotty/Harper roles)
- Reflect new architecture layers: Tool Prompt Snippets and Shared Context
- Align repository structure diagram with current filesystem layout

docs/tools/github.md

@@ -0,0 +1,28 @@
+# GitHub
+
+> GitHub repository access via GitHub Copilot MCP.
+
+- **MCP server name:** `github` (GitHub Copilot MCP, hosted at `api.githubcopilot.com`)
+- **Prompt snippet:** [prompts/tools/github.md](../../prompts/tools/github.md)
+
+## What It Is
+
+GitHub MCP gives agents access to repositories on GitHub.com — Robert's own repos, plus public repos when reference is needed. Powered by GitHub's Copilot MCP service.
+
+## What It's Good For
+
+- Reading source from public projects (libraries, frameworks, reference implementations)
+- Inspecting issues and PRs on GitHub-hosted repos
+- Pulling context from a project Robert has on GitHub specifically (vs. Gitea)
+- Cross-checking how an upstream library actually behaves vs. how its docs describe it
+
+## What It's Not Good For
+
+- Repos hosted on `git.helu.ca` — that's Gitea
+- Bulk operations or rate-limited heavy workflows — GitHub's API limits apply
+- Anything that should be local — use Kernos in a clone for active development
+
+## Known Gotchas
+
+- **Auth scope.** The MCP server's token determines what it can see. Private repos require correct token scope; expect "not found" errors if scope is wrong.
+- **Rate limits are real.** Hitting the GitHub API too aggressively will produce 403/429 responses. The MCP layer doesn't magically hide this.