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

docs/api-keys-and-mcp.md

@@ -86,8 +86,7 @@ table here. The tools are grouped by family:
 | Tasks | `create_task`, `update_task`, `add_task_log`, `start_planning` | Actionable work + plans |
 | Projects / Milestones | `enter_project`, `get_project`, `create_milestone`, … | Containers and outcomes |
 | Search / Recall | `search`, `get_recent`, `list_tags` | Semantic + structured recall |
-| Typed entities | `create_person`, `create_place`, `create_list`, … | Structured records |
-| Events | `create_event`, `list_events`, `update_event`, … | Calendar |
+| Systems | `create_system`, `list_systems`, `list_system_records` | Reusable per-project subsystems/areas |
 | Rulebooks | `list_always_on_rules`, `list_rules`, `create_rule`, `create_project_rule`, `subscribe_project_to_rulebook`, … | Engineering/workflow rules |
 | Processes | `list_processes`, `get_process`, `create_process` | Saved prompts/workflows |
 | Trash | `list_trash`, `restore`, `purge_trash` | Recoverable deletes |