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/time.md

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+# Time
+
+> Current time and timezone.
+
+- **MCP server name:** `time` (runs locally)
+- **Prompt snippet:** [prompts/tools/time.md](../../prompts/tools/time.md)
+
+## What It Is
+
+A tiny tool that does one thing: tell the agent what time it is, in a given timezone. Trivial in description, essential in practice — LLMs don't know the current date, and conversations can span days or months.
+
+## What It's Good For
+
+- Checking today's date before timestamping anything (graph nodes, file names, messages)
+- Building IDs that include a date component (`note_2026-05-20_…`)
+- Reasoning about "recent" vs "old" in any context where the answer depends on now
+- Timezone conversions when scheduling or interpreting log timestamps
+
+## What It's Not Good For
+
+- Anything that isn't time. It's a single-purpose tool.
+
+## Known Gotchas
+
+- **Don't assume the date.** Always check before using a date in something that gets stored — node IDs, message slugs, file names, journal entries. The agent's training cutoff is not "now."
+- **Timezone defaults vary.** Specify the timezone explicitly when it matters (UTC for logs, local time for user-facing).