docs: switch context7 to official plugin; remove three manual MCP entries

Context: user previously had context7 MCP server registered manually in
three places (~/.claude/settings.json + two in ~/.claude.json), with the
CONTEXT7_API_KEY in HTTP-header form. Replaced with the official
context7@claude-plugins-official plugin.

What changed (outside the repo):
- ~/.claude/plugins/cache/.../context7/unknown/.mcp.json — added
  "--api-key" CLI flag to args (Upstash docs recommend this for stdio).
- ~/.claude/settings.json — removed top-level mcpServers.context7.
- ~/.claude.json — removed top-level mcpServers.context7 and a legacy
  project-scoped entry under projects[snolla-admin-ui].

Backups saved with suffix .bak-20260428-114532.

What changed in the repo (this commit):
- .wiki/concepts/context7-setup.md — new page documenting where the key
  lives, the /plugin update gotcha, and the rollback path.
- .wiki/index.md, log.md — linked / logged.
- .tasks/STATUS.md — task moved to Done.

Plugin takes effect after Claude Code restart; current session still uses
the legacy HTTP transport (verified via smoke test on resolve-library-id).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.wiki/index.md

@@ -14,6 +14,7 @@ Catalog of all wiki pages. One line per page, organized by type. Updated on ever
 
 - [active-platform-decision.md](concepts/active-platform-decision.md) — why `active-platform` is a skill (not a memory entry); why default = Windows; how it's wired into `project-bootstrap`
 - [build-notes.md](concepts/build-notes.md) — why `build.ps1` exists alongside `build.sh`; PS 5.1 backslash-in-zip gotcha; how to extract a `.skill`
+- [context7-setup.md](concepts/context7-setup.md) — switched context7 from manual MCP entries to the official plugin; API key now lives in the plugin's `.mcp.json` as `--api-key`; re-apply after `/plugin update`
 - [repo-layout.md](concepts/repo-layout.md) — flat `skills/`, committed `dist/`, bash + PowerShell scripts; install model
 - [wiki-realignment.md](concepts/wiki-realignment.md) — fixing `project-bootstrap` to create the Karpathy-canonical wiki layout