Added plugin/add-on system

Plugins live in plugins/<name>/ with a manifest.json and a LabPlugin
subclass. Enabled/disabled in Settings > Plugins tab; state persists in
plugins/enabled.json and in .labdaq profiles (loading a profile
enables/disables plugins to match). Plugins can contribute toolbar
buttons, BaseDevice instances (auto-wired into acquisition pipeline),
custom signal filter classes, a settings widget, and profile state via
get_save_state/apply_save_state. Load errors now report the exact
failing stage (file not found, class missing, on_load crash).
Includes example plugin skeleton and docs/plugin-development.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

3 files changed, 113 insertions, 0 deletions

diff --git a/plugins/example/__pycache__/plugin.cpython-312.pyc b/plugins/example/__pycache__/plugin.cpython-312.pyc
new file mode 100644
index 0000000..c31b466
--- /dev/null
+++ b/plugins/example/__pycache__/plugin.cpython-312.pyc
diff --git a/plugins/example/manifest.json b/plugins/example/manifest.json
new file mode 100644
index 0000000..a5af87d
--- /dev/null
+++ b/plugins/example/manifest.json
@@ -0,0 +1,8 @@
+{
+  "plugin_id":   "example",
+  "name":        "Example Plugin",
+  "version":     "1.0.0",
+  "description": "Skeleton showing all plugin integration points. Safe to delete.",
+  "author":      "Your Name",
+  "entry_point": "plugin.ExamplePlugin"
+}
diff --git a/plugins/example/plugin.py b/plugins/example/plugin.py
new file mode 100644
index 0000000..e5fbb8e
--- /dev/null
+++ b/plugins/example/plugin.py
@@ -0,0 +1,105 @@
+"""
+plugins/example/plugin.py
+
+Skeleton plugin — shows every integration point.
+Copy this directory, rename it, update manifest.json, and fill in your logic.
+"""
+
+from __future__ import annotations
+from typing import Any, Dict, List, Optional, Type
+
+from PyQt6.QtWidgets import QLabel, QWidget
+
+# LabDAQ imports available at runtime
+from plugins.base_plugin import LabPlugin, PluginAction, PluginContext
+
+
+class ExamplePlugin(LabPlugin):
+
+    # ── Metadata ──────────────────────────────────────────────────────────
+
+    @property
+    def plugin_id(self) -> str:
+        return "example"
+
+    @property
+    def name(self) -> str:
+        return "Example Plugin"
+
+    @property
+    def version(self) -> str:
+        return "1.0.0"
+
+    @property
+    def description(self) -> str:
+        return "Skeleton showing all plugin integration points."
+
+    @property
+    def author(self) -> str:
+        return "Your Name"
+
+    # ── Lifecycle ─────────────────────────────────────────────────────────
+
+    def on_load(self, context: PluginContext) -> None:
+        self._ctx = context
+        # e.g. start a background thread, open a camera, etc.
+
+    def on_unload(self) -> None:
+        # Release resources — called when user disables plugin
+        pass
+
+    # ── Toolbar ───────────────────────────────────────────────────────────
+
+    def get_toolbar_actions(self) -> List[PluginAction]:
+        return [
+            PluginAction(
+                label     = "Example",
+                icon      = "🔌",
+                tooltip   = "Open example plugin window",
+                checkable = True,
+                callback  = self._on_toolbar_click,
+            )
+        ]
+
+    def _on_toolbar_click(self, checked: bool):
+        # Open / close your plugin window here
+        pass
+
+    # ── Devices ───────────────────────────────────────────────────────────
+
+    def get_devices(self) -> list:
+        # Return BaseDevice instances — they are auto-added to the registry
+        # and AcquisitionEngine so their channels appear as normal signals.
+        #
+        # Example (uncomment and adapt):
+        #   from devices.analog_input import AnalogInputDevice
+        #   return [AnalogInputDevice("my_plugin_ai", num_channels=2, simulate=True)]
+        return []
+
+    # ── Custom filters ────────────────────────────────────────────────────
+
+    def get_filter_classes(self) -> Dict[str, Type]:
+        # Return {type_name: FilterBase subclass} for custom pipeline filters.
+        #
+        # Example:
+        #   from .my_filter import MyFilter
+        #   return {"my_filter": MyFilter}
+        return {}
+
+    # ── Settings widget ───────────────────────────────────────────────────
+
+    def get_settings_widget(self) -> Optional[QWidget]:
+        # Return a QWidget shown in Settings > Plugins when this plugin is enabled.
+        lbl = QLabel("No settings for this plugin.")
+        lbl.setObjectName("traceSource")
+        return lbl
+
+    # ── Profile persistence ───────────────────────────────────────────────
+
+    def get_save_state(self) -> Dict[str, Any]:
+        # Return JSON-serialisable dict saved with .labdaq profiles.
+        return {}
+
+    def apply_save_state(self, state: Dict[str, Any]) -> None:
+        # Restore plugin state when a profile is loaded.
+        pass