docs(scribe): true up plugin + MCP docs after calendar/entity removal

Milestone #194 plugin/docs slice.

- plugin.json: "second brain" framing -> "system-of-record"; bump
  0.1.11 -> 0.1.12 (any plugin/ change must bump the manifest, issue #1040)
- plugin/README.md + using-scribe SKILL + scribe_static_context: drop
  events/typed-entities from the surface lists; "second brain" -> "system
  of record" in the SessionStart context Claude reads each session
- docs/api-keys-and-mcp.md: drop the Typed-entities + Events MCP tool rows,
  add the Systems row
- README.md: rewrite the stale front-matter (chat/RAG/calendar/weather/push
  described a pre-pivot product) to the current Claude-driven work store

Deeper pre-pivot doc-rot in docs/features.md + docs/api-reference.md
(chat/journal/weather/web-research) is tracked separately as an issue.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BPtbSzA4JLMAKgFZ8VTg7Q

plugin/hooks/scribe_static_context.md

@@ -1,7 +1,7 @@
-# Scribe — your second brain and system of record
+# Scribe — your system of record
 
-This environment has the **Scribe** plugin: the operator's self-hosted second
-brain (notes, tasks, projects, milestones, rules) reachable through the
+This environment has the **Scribe** plugin: the operator's self-hosted system
+of record (notes, tasks, projects, milestones, rules) reachable through the
 `scribe` MCP tools. Treat Scribe — **not local files** — as the source of truth
 for the operator's work, and as your own working memory across sessions.