Phase 7B: per-plugin Alembic chains for bundled plugins

Each of the six bundled plugins (computers, equipment, network,
notifications, printers, usb) now has its own Alembic chain with a
baseline migration. Sister sites adopting one of these plugins can
manage its schema via `flask plugin migrate <name>` instead of relying
on db.create_all to bootstrap everything.

Existing single-site deploys that bootstrap via db.create_all continue
to work unchanged. The chains coexist; the bootstrap path stays the
operator's choice.

Framework
- shopdb/plugins/alembic_template.py: shared env.py logic + helpers.
  PLUGIN_TABLE_OWNERS pins which tables belong to which plugin (explicit
  registry, not import-side-effect). _get_plugin_metadata filters
  db.metadata to only the named plugin's tables. create_plugin_tables /
  drop_plugin_tables emit DDL via SQLAlchemy CreateTable so the table
  definitions stay sourced from the models, not duplicated.
- shopdb/plugins/__init__.py: PluginManager.upgrade_all_plugins() runs
  pending migrations across every discovered plugin and returns a status
  dict. Idempotent (Alembic skips applied revisions).

CLI
- `flask plugin upgrade-all` runs pending migrations for every plugin.
  Used on a fresh deploy after the core schema is in place.

Per-plugin scaffolding
- plugins/{computers,equipment,network,notifications,printers,usb}/
  migrations/{alembic.ini, env.py, script.py.mako, versions/0001_baseline.py}
- Each env.py is a 5-line shim that sets PLUGIN_NAME and delegates to
  the shared template. Each 0001_baseline calls create_plugin_tables(name)
  / drop_plugin_tables(name); no duplication of column definitions.

Tests
- tests/test_plugin_migrations.py (18 cases): every bundled plugin has
  an entry in PLUGIN_TABLE_OWNERS, has the on-disk Alembic scaffolding,
  and the filtered MetaData contains every owned table (catches drift
  between the template's table list and what the models declare).
- 129 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

shopdb/plugins/__init__.py

@@ -71,6 +71,34 @@ class PluginManager:
         for name, plugin in plugins.items():
             self._register_plugin_components(plugin)
 
+    def upgrade_all_plugins(self) -> Dict[str, str]:
+        """Run pending Alembic migrations for every loaded plugin.
+
+        Returns {plugin_name: 'ok'|'no-migrations'|<error str>}. Skips
+        plugins with no migrations/ directory. Use from the CLI
+        (`flask plugin upgrade-all`) on a fresh deploy after the core
+        schema is in place; existing deploys that still use db.create_all
+        can ignore this and continue to do so.
+        """
+        results: Dict[str, str] = {}
+        if not self.migration_manager:
+            return results
+        plugin_names = list(self.registry.list_installed().keys()) \
+            if hasattr(self.registry, 'list_installed') else []
+        if not plugin_names:
+            # Fall back to whatever the loader found on disk.
+            plugin_names = self.loader.discover_plugins()
+        for name in plugin_names:
+            if not self.migration_manager.has_pending_migrations(name):
+                results[name] = 'no-migrations'
+                continue
+            try:
+                ok = self.migration_manager.run_plugin_migrations(name)
+                results[name] = 'ok' if ok else 'failed'
+            except Exception as ex:
+                results[name] = f'error: {ex}'
+        return results
+
     def _register_plugin_components(self, plugin: BasePlugin) -> None:
         """Register plugin's blueprint, models, CLI commands, etc."""
         # Register blueprint