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/concepts/context7-setup.md

@@ -0,0 +1,73 @@
+---
+title: "context7 setup: official plugin + API key"
+type: concept
+updated: 2026-04-28
+---
+
+# context7 setup: official plugin + API key
+
+_2026-04-28._
+
+## Where the MCP server is now registered
+
+Single source: the official plugin **`context7@claude-plugins-official`**.
+
+The plugin's `.mcp.json` (after install) lives at:
+```
+~/.claude/plugins/cache/claude-plugins-official/context7/<version>/.mcp.json
+```
+
+For this user the version slug is `unknown` (marketplace plugin without a tagged release).
+
+## API-key injection
+
+The `@upstash/context7-mcp` npm package, run via stdio, accepts the key as a CLI flag (per Upstash docs at <https://context7.com/docs/resources/all-clients>):
+
+```json
+{
+  "context7": {
+    "command": "npx",
+    "args": ["-y", "@upstash/context7-mcp", "--api-key", "ctx7sk-..."]
+  }
+}
+```
+
+We injected the user's existing key (previously in HTTP-header form) into this `args` array. Header / `env` block forms are also supported, but the CLI flag is what Upstash recommends for stdio.
+
+## What was removed
+
+Three manual MCP registrations were deleted:
+
+| File | Where | Had API key? |
+|---|---|---|
+| `~/.claude/settings.json` | top-level `mcpServers.context7` | yes (header) |
+| `~/.claude.json` | top-level `mcpServers.context7` | yes (header) |
+| `~/.claude.json` | `projects["…/snolla-admin-ui"].mcpServers.context7` | no (legacy) |
+
+Backups saved with suffix `.bak-YYYYMMDD-HHMMSS` next to each file.
+
+## ⚠️ Plugin-update gotcha
+
+`/plugin update context7@claude-plugins-official` (or a fresh re-install) **will overwrite** the plugin's `.mcp.json` from the marketplace cache, dropping the `--api-key` flag. After any plugin update, re-apply the edit:
+
+```bash
+# inspect
+cat ~/.claude/plugins/cache/claude-plugins-official/context7/<version>/.mcp.json
+
+# if --api-key is missing, re-inject
+```
+
+The marketplace upstream of the plugin lives at `anthropics/claude-plugins-official/external_plugins/context7/.mcp.json` and is two lines — unlikely to change often, but we should expect to re-apply the flag after updates.
+
+## Restart required to take effect
+
+Claude Code reads MCP server configs at session start. The session in which this change was made keeps its old (HTTP-transport) connection until a restart. After restart, the plugin's stdio invocation takes over.
+
+## Why this matters
+
+Manual MCP entries in `~/.claude.json` / `settings.json` are easy to:
+- duplicate accidentally (we had three for one server)
+- forget about when sharing config
+- drift from the canonical version
+
+The plugin centralizes the registration and gets versioned through the marketplace. The price is a single edit-after-update for the API key.