feat(plugins): show marketplace details and add an Update button

[pjdoland]

Summary

Plugin marketplace rows on the Plugins tab now show the marketplace's description, version, and a plugin-count + comma-separated name list trimmed with +N more. Each row has an Update button that runs claude plugin marketplace update <name> and refreshes the panel.

Solution

Backend (notebook_intelligence/plugin_manager.py): list_marketplaces enriches each entry with description, version, plugin_count, and plugin_names pulled from the cached ~/.claude/plugins/marketplaces/<name>/.claude-plugin/marketplace.json. Both the documented top-level fields (description, version) and the legacy metadata.description / metadata.version shape are read for backward compatibility per the Claude Code marketplace docs. New update_marketplace(name) method shells out to claude plugin marketplace update <name> with optional GitHub-token injection via env (never argv).

The manifest read is bounded by a 1 MiB size cap to keep a hostile or corrupt marketplace.json from OOMing the server on a list-marketplaces call. The read-failure path swallows OSError (including PermissionError and FileNotFoundError), ValueError, and UnicodeDecodeError so one bad manifest cannot abort the whole list endpoint. _read_marketplace_manifest also validates the marketplace name against the same path-traversal / NUL / leading-dash check used by list_marketplace_plugins, so a CLI-returned name like ../evil is rejected at the manifest-read layer rather than relying on upstream sanitization.

Enrichment overlay rules:

• description and version: a non-empty CLI value wins; an empty-string CLI value falls through to the manifest, so a future Claude CLI release that surfaces these fields server-side is honored.
• plugin_count and plugin_names: treated as a coupled pair. If the CLI surfaces either, both come from the CLI; otherwise both come from the manifest. Coupling prevents a row that shows "42 plugins: alpha, beta" because the count came from one source and the names from another.

Handler (notebook_intelligence/extension.py): new PluginsMarketplaceUpdateHandler at POST plugins/marketplace/<name>/update, registered ahead of the catch-all detail route and inheriting PluginsBaseHandler so @tornado.web.authenticated and the claude_plugins_management policy gate both apply.

Client (src/api.ts): IPluginMarketplaceInfo gains optional description, version, plugin_count, plugin_names. New updatePluginMarketplace(name) method.

UI (src/components/plugins-panel.tsx + style/base.css): row renders the name with a v<version> pill, the description (when present), the source string (existing), and a plugin summary "N plugins: a, b, c, +D more" via a new exported summarizePluginNames helper. Visible cap defaults to 5; the row CSS also has text-overflow: ellipsis as a width-based fallback. The plugin line is omitted entirely when the manifest hasn't been cached yet so a just-added marketplace doesn't render a misleading "no plugins." Buttons: Update (jp-mod-accept, matching its non-destructive intent) and Remove (jp-mod-reject). The busy state disables both buttons in tandem with verb-specific labels ("Updating…", "Removing…").

Testing

• tests/test_plugin_manager.py: pytest cases covering top-level + metadata.* enrichment, override-on-truthy semantics parametrized across description / version / plugin_count / plugin_names, plugin_count/plugin_names coupling (CLI sets one but not both → both still come from CLI), oversize-manifest rejection, unreadable-dir skip, missing-manifest skip, path-traversal rejection in a CLI-returned name, the new update CLI invocation, GitHub-token injection on update, and path-traversal rejection on the update name argument.
• tests/ts/plugins-panel.test.tsx: jest cases on the marketplace row (description / version / plugin summary, +N truncation, empty-state copy, manifest-not-loaded omission, update button calls API, error path) plus summarizePluginNames semantics, plus the busy-state contract (both row buttons disabled, verb-specific labels) while an update is in flight.
• Full suites: pytest 788 pass, tsc clean, prettier clean, jest clean.

Risks / follow-ups

• Behavior change: the marketplace list response gains four optional fields. Existing clients ignore them; the new client renders the richer row. No backwards-incompatible field renames.
• Manual UI walk-through deferred: I couldn't start a local JupyterLab server autonomously (the auto-classifier blocked it). The jest suite covers the row layout, but a real-browser pass against a freshly-added marketplace (Playwright or hand) would catch CSS regressions the unit tests can't see.
• Token injection on local sources: update_marketplace injects GITHUB_TOKEN unconditionally. The token never lands in argv (env only), and the claude subprocess only forwards it to git when the upstream is GitHub, so non-GitHub sources see an unused env var. Deliberate to avoid re-reading the source from disk on every update; comment in-tree calls this out.
• No --scope on update: marketplace names are unique within the global Claude plugin cache, so claude plugin marketplace update <name> is scope-free by design.

Closes #289.