feat: add mmd-it marketplace + mmd-workspace plugin (4 MMD skills)

Org-wide Claude Desktop plugin marketplace for MMD Group IT. Adds the
mmd-it marketplace manifest and the mmd-workspace plugin
(installationPreference: required) carrying four skills grounded in
real MMD material: mmd-document-style, mmd-email-style,
mmd-it-support, mmd-data-handling. Public repo, no secrets — MCP
credentials are delivered separately via managedMcpServers.

README.md

@@ -1,3 +1,42 @@
 # claude-plugins
 
-MMD Group IT Claude Desktop plugin marketplace — org-wide skills and plugin distribution. Public by design: end-user devices clone with no credential. No secrets live here.
+MMD Group IT's Claude Desktop plugin marketplace. Every MMD device with Claude Desktop
+configured for MMD's third-party inference bootstrap clones this repository and installs the
+`mmd-workspace` plugin automatically (`installationPreference: required`), giving every MMD
+user the same skills without per-device setup.
+
+This repository is **public and contains no secrets by design** — end-user devices clone it
+without any git credential, since MMD's internal Gitea repositories are private and devices in
+the field have none configured. Anything that needs a credential (MCP server URLs, API keys,
+tenant IDs) is delivered separately, per signed-in user, through the `managedMcpServers` field
+of the bootstrap response served at `claude-config.baobab-ts.com/user/bootstrap` — never
+through this repo. Do not add credentials, tokens, or API keys here, ever.
+
+## Structure
+
+```
+.claude-plugin/marketplace.json      marketplace manifest (name: mmd-it)
+plugins/mmd-workspace/
+  .claude-plugin/plugin.json         plugin manifest (installationPreference: required)
+  version.json                       bump this to push an update to every device
+  skills/
+    mmd-document-style/SKILL.md      MMD-branded Word/PDF/PowerPoint house style
+    mmd-email-style/SKILL.md         MMD email conventions incl. [MMD #ticket] + helpdesk copy
+    mmd-it-support/SKILL.md          how to raise/track an IT request via MMD Support (GLPI)
+    mmd-data-handling/SKILL.md       what may/may not go into the assistant given MMD's gateway
+```
+
+## Rolling out an update
+
+1. Edit the plugin content on a feature branch, open a PR, merge to `main`.
+2. Bump `plugins/mmd-workspace/version.json`.
+3. Update the `ref` in `allowedPluginMarketplaces` (in `mmd-ops`'
+   `manifests/claude-config-server/configmap.yaml`) to the new commit's full 40-character SHA —
+   Claude Desktop refuses to auto-install from a branch or tag name.
+4. Push that change through `mmd-ops` (feature branch + PR + merge); ArgoCD rolls the config
+   server.
+
+Devices pick up the new revision on next launch or plugin-settings refresh.
+
+See `https://claude.com/docs/third-party/claude-desktop/extensions` for the marketplace/plugin
+schema this repository follows.