fix(plugin): add marketplace manifest so the documented install works

The repo shipped a plugin manifest at tools/claude/.claude-plugin/plugin.json
but no marketplace catalog, so '/plugin marketplace add stijnvanhulle/template'
failed with 'Marketplace file not found'. Add .claude-plugin/marketplace.json
at the repo root pointing the 'plugin' entry at ./tools/claude.

Marketplace names cannot contain a slash, so the install reference is the
manifest name 'stijnvanhulle-template', not the owner/repo slug. Update the
README, AGENTS.md, and tools/claude/README.md to 'plugin@stijnvanhulle-template'.

Author: claude

.claude-plugin/marketplace.json

@@ -0,0 +1,18 @@
+{
+  "$schema": "https://json.schemastore.org/claude-code-marketplace-manifest.json",
+  "name": "stijnvanhulle-template",
+  "owner": {
+    "name": "stijnvanhulle",
+    "url": "https://github.com/stijnvanhulle"
+  },
+  "metadata": {
+    "description": "Marketplace for the stijnvanhulle toolkit plugin."
+  },
+  "plugins": [
+    {
+      "name": "plugin",
+      "source": "./tools/claude",
+      "description": "Spec-driven workflow, writing-voice skills, code-reviewer agent, and shared TypeScript-monorepo conventions."
+    }
+  ]
+}

AGENTS.md

@@ -80,7 +80,7 @@ symlink to it so Claude Code, Gemini CLI, and GitHub Copilot pick up the
 same content. The shared toolset (skills, commands, code-reviewer agent,
 output styles, and conventions) lives in `tools/claude/`, which is also
 packaged as a Claude Code plugin (installable as
-`plugin@stijnvanhulle/template`). The `.claude/` and `.agents/skills/`
+`plugin@stijnvanhulle-template`). The `.claude/` and `.agents/skills/`
 paths used by the workspace symlink into that folder, so the template repo
 and any project that installs the plugin run the same content.
 Workspace-only pieces (hooks and `settings.json`) stay under `.claude/`.

README.md

@@ -30,7 +30,7 @@ Agent Skills, and uses symlinks so every tool reads from one source instead of d
 
 `AGENTS.md` is the canonical instruction file. The shared toolset (skills, commands,
 code-reviewer agent, output styles, and conventions) lives in `tools/claude/`, which doubles as
-a Claude Code plugin (installable as `plugin@stijnvanhulle/template`). The workspace paths under `.claude/` and `.agents/`
+a Claude Code plugin (installable as `plugin@stijnvanhulle-template`). The workspace paths under `.claude/` and `.agents/`
 symlink into that folder, so the template repo and any project that installs the plugin run
 the same content from a single source of truth. See [tools/claude/README.md](tools/claude/README.md)
 for install steps.

tools/claude/README.md

@@ -6,8 +6,8 @@ the always-on rules (code style, JSDoc, markdown, security, testing).
 
 The toolkit is extracted from [stijnvanhulle/template](https://github.com/stijnvanhulle/template)
 so the same content powers the template repo itself and any project that installs
-the plugin. It is published under the plugin name `plugin`, so the install reads as
-`plugin@stijnvanhulle/template`.
+the plugin. It is published under the plugin name `plugin` from the `stijnvanhulle-template` marketplace, so the install reads as
+`plugin@stijnvanhulle-template`.
 
 ## What you get
 
@@ -39,7 +39,7 @@ spec-driven formatting (`plan`), and a diagrams-first layout (`diagrams-first`).
 ```bash
 # add this repo as a marketplace, then install the plugin
 /plugin marketplace add stijnvanhulle/template
-/plugin install plugin@stijnvanhulle/template
+/plugin install plugin@stijnvanhulle-template
 ```
 
 To try it locally before publishing: