fix(dev): link-github links plugins from the ledmatrix-plugins monorepo

link-github <name> cloned https://github.com/ChuckBuilds/ledmatrix-<name>.git,
and those per-plugin repositories no longer exist: official plugins are
directories in the ledmatrix-plugins monorepo. It now clones (or pulls) the
monorepo once into the dev directory, finds plugins/<name>,
plugins/ledmatrix-<name> or the plugin whose manifest id is <name>, and
links it under its manifest id. With an explicit repo URL it still links a
single-repository plugin as before.

dev_plugins.json: github_user is honoured again (monorepo owner, e.g. a
fork), plus plugins_repo and plugins_branch; github_pattern, which was
documented but never read, is dropped and warned about. Ships
dev_plugins.json.example and git-ignores dev_plugins.json, both of which
the guide promised. Reading JSON falls back to python3 when jq is missing
(get_plugin_id silently returned nothing without jq).

update/status/list find the git checkout above a monorepo plugin
directory (its .git is not in the plugin dir), and update pulls a shared
checkout once. status no longer exits 1 when nothing is broken.

Docs: PLUGIN_DEVELOPMENT_GUIDE (quick start, link-github, configuration,
workflow, store integration, hello-world link, submission), and the
nonexistent scripts/git-hooks/pre-push-plugin-version and
scripts/bump_plugin_version.py replaced with the real rule: bump the
manifest version and run update_registry.py. scripts/dev/README.md and
CLAUDE.md updated to match.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

dev_plugins.json.example

@@ -0,0 +1,6 @@
+{
+  "dev_plugins_dir": "~/.ledmatrix-dev-plugins",
+  "github_user": "ChuckBuilds",
+  "plugins_repo": "ledmatrix-plugins",
+  "plugins_branch": "main"
+}