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/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "scribe",
-  "description": "Scribe second brain for Claude Code: MCP tools over your notes/tasks/projects/rules, a session-start push channel that surfaces your always-on rules + active-project context, process-skills (writing-plans, systematic-debugging, verification, brainstorming), and your saved Scribe Processes auto-surfaced as skills (/scribe:sync). Replaces superpowers + file-memory with one app-backed plugin.",
-  "version": "0.1.11",
+  "description": "Scribe system-of-record for Claude Code: MCP tools over your notes/tasks/projects/rules, a session-start push channel that surfaces your always-on rules + active-project context, process-skills (writing-plans, systematic-debugging, verification, brainstorming), and your saved Scribe Processes auto-surfaced as skills (/scribe:sync). Replaces superpowers + file-memory with one app-backed plugin.",
+  "version": "0.1.12",
   "author": { "name": "Bryan Van Deusen" },
   "mcpServers": {
     "scribe": {