Rename the import package app to fluksio

A wheel whose top-level module is `app` collides with anything else in a
user's venv, so the package that is about to be published takes the name
it is published under. Only the Python package moves; the repo, the
Docker WORKDIR and the compose project keep theirs.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/fluksio/flow/plugins.py

@@ -0,0 +1,77 @@
+"""Loading connector plugins from installed packages.
+
+A connector is an ordinary Python package that advertises its node class under
+the ``fluksio.node_types`` entry point group. The entry point's name is the
+node type as it appears on the canvas, and the package's own metadata — name
+and version — is the manifest; there is no second format to keep in step.
+
+Discovery happens once, at startup: a connector's code is imported, and Python
+does not re-import a changed module, so a rescan would promise more than it
+delivers. Installing or upgrading one means restarting the engine.
+"""
+
+from __future__ import annotations
+
+import logging
+from importlib.metadata import entry_points
+
+from fluksio.flow.connector import CONTRACT_VERSION, ConnectorNode
+
+logger = logging.getLogger(__name__)
+
+ENTRY_POINT_GROUP = "fluksio.node_types"
+
+
+def load_plugins() -> list[str]:
+    """Register every installed connector. Returns the type names it added."""
+    from fluksio.flow.controller import NODE_TYPES, NodeType, _schema_of
+
+    added: list[str] = []
+    for entry in entry_points(group=ENTRY_POINT_GROUP):
+        if entry.name in NODE_TYPES:
+            logger.warning(
+                "Ignoring connector '%s': that node type already exists", entry.name
+            )
+            continue
+        try:
+            cls = entry.load()
+        except Exception:
+            logger.exception("Could not load connector '%s'", entry.name)
+            continue
+
+        if not (isinstance(cls, type) and issubclass(cls, ConnectorNode)):
+            logger.warning(
+                "Ignoring connector '%s': %r is not a ConnectorNode", entry.name, cls
+            )
+            continue
+        # Checked on the class itself: inheriting a version from a base class
+        # would let a connector written against an older contract look current.
+        if cls.__dict__.get("contract") != CONTRACT_VERSION:
+            logger.warning(
+                "Ignoring connector '%s': written for contract version %s, "
+                "this engine speaks %s",
+                entry.name,
+                cls.__dict__.get("contract"),
+                CONTRACT_VERSION,
+            )
+            continue
+
+        NODE_TYPES[entry.name] = NodeType(
+            title=cls.title or entry.name,
+            description=cls.description,
+            cls=cls,
+            params_schema=_schema_of(cls),
+            plugin=_provenance(entry),
+        )
+        added.append(entry.name)
+        logger.info("Loaded connector '%s' from %s", entry.name, _provenance(entry))
+
+    return added
+
+
+def _provenance(entry: object) -> str:
+    """Which package this node type came from, for the editor to show."""
+    dist = getattr(entry, "dist", None)
+    if dist is None:
+        return "unknown"
+    return f"{dist.name} {dist.version}"