feat(plugin-detail): show Markdown plugin details on bundle and market entry pages

Plugins bundle pages and Discover entry pages show the plugin's long
description first, as Markdown with images, in a height-limited region
without its own heading. The document is the file locale meta.detail
names, otherwise the package README, otherwise (market entries only)
the declared repository's README.

The new dsh-plugin-detail library selects documents and reads local
package directories and npm file CDNs without state. plugin-manager
reads installed and offered bundles through readBundleDetail; plugin-market
reads market entries through readEntryDetail, single-file APIs, and a
size-limited partial clone cache serialized across processes. Raw HTML is
omitted, relative links stay text, and relative images load from Host
routes with a sandbox CSP.

tsconfig.base.json

@@ -231,6 +231,7 @@
       "@deepseek-ai/dsh-plugin-manager/tools": ["./packages/boot/plugin-manager/src/tools.ts"],
       "@deepseek-ai/dsh-plugin-market/types": ["./packages/boot/plugin-market/src/types.ts"],
       "@deepseek-ai/dsh-plugin-market/tools": ["./packages/boot/plugin-market/src/tools.ts"],
+      "@deepseek-ai/dsh-plugin-detail/types": ["./packages/util/plugin-detail/src/types.ts"],
       "@deepseek-ai/dsh-tool-cordis/host": ["./packages/extensions/tool-cordis/src/host.ts"],
       "@deepseek-ai/dsh-host-plugin-inventory": ["./packages/host/plugin-inventory/src"],
       "@deepseek-ai/dsh-host-plugin-inventory/types": ["./packages/host/plugin-inventory/src/types.ts"],
@@ -441,6 +442,7 @@
       "@deepseek-ai/dsh-permission-presets": ["./packages/interaction/permission-presets/src"],
       "@deepseek-ai/dsh-persona": ["./packages/preset/persona/src"],
       "@deepseek-ai/dsh-plan-mode": ["./packages/plan/plan-mode/src"],
+      "@deepseek-ai/dsh-plugin-detail": ["./packages/util/plugin-detail/src"],
       "@deepseek-ai/dsh-plugin-market": ["./packages/boot/plugin-market/src"],
       "@deepseek-ai/dsh-plugin-market-index": ["./packages/util/plugin-market-index/src"],
       "@deepseek-ai/dsh-plugin-package-inventory-deepseek": ["./packages/llm/plugin-package-inventory-deepseek/src"],