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/skills/using-scribe/SKILL.md

@@ -5,8 +5,8 @@ description: Use at the START of every session, and before answering anything ab
 
 # Using Scribe
 
-Scribe is the operator's self-hosted second brain (notes, tasks, issues,
-projects, milestones, systems, events, typed entities) and rulebook, reachable
+Scribe is the operator's self-hosted system of record (notes, tasks, issues,
+projects, milestones, systems) and rulebook, reachable
 through the bundled `scribe` MCP server. Its value is mostly in what it
 **already holds** — so make reading it a reflex, not something you wait to be
 asked for.