feat: migrate distributed nodes to native ComfyUI V3 API (#94)

* feat: migrate distributed nodes to native ComfyUI V3 API

* fix: hide Distributed Value backing fields in Nodes 2.0

Use native widget visibility without converting backing fields into sockets. Preserve widget types, serializers and options identity; cover edits, reload, worker refresh and linked widgets.

docs/v3-migration.md

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+# Native V3 node API
+
+The package registers one `ComfyExtension` through `comfy_entrypoint()` and
+imports the versioned `comfy_api.v0_0_2` API. Use a ComfyUI version that provides
+that API; there is no V1 registration fallback.
+
+## Compatibility
+
+- All eight node IDs, display names, categories, visible input order, defaults
+  and output order are retained. Existing execution algorithms remain in the
+  private collector, utilities and upscale modules.
+- The image/audio dividers explicitly declare ten typed outputs. Their existing
+  frontend extensions still show only the selected number of outputs. This
+  replaces the V1 `ByPassTypeTuple` indexing workaround without changing saved
+  IMAGE/AUDIO socket indices or the ten returned values.
+- Standard hidden context uses `cls.hidden`. Worker/orchestration metadata keeps
+  its existing prompt-input names and Python defaults via `accept_all_inputs`;
+  it does not become visible widgets.
+- The collector retains list-input handling. Upscale retains its always-changing
+  fingerprint and creates a private runtime helper for each V3 execution, so
+  mutable helper state is not attached to sanitized V3 class clones.
+- Routes, distributed state and the existing worker startup/shutdown hooks are
+  initialized by `runtime/bootstrap.py` during `ComfyExtension.on_load()`.
+  Worker mode still suppresses automatic worker launch. `distributed.py` is no
+  longer an entrypoint.
+
+## Verification
+
+Run ordinary unit tests from this repository:
+
+```bash
+python -m pytest tests -q -o addopts=
+```
+
+Opt into real-framework acceptance using a ComfyUI checkout and its interpreter:
+
+```bash
+COMFYUI_SOURCE_ROOT=/path/to/ComfyUI \
+  /path/to/ComfyUI/.venv/bin/python -m pytest tests -q -o addopts=
+```
+
+The acceptance subprocess uses CPU mode and the real ComfyUI loader, input
+parser, V3 class preparation, prompt validation and `PromptExecutor`. It compares
+all node schemas with the V1 fixture, checks all five bundled workflows' node
+IDs and socket/link contracts, exercises injected worker metadata, image/audio
+lists, collector aggregation and divider outputs, rejects invalid upscale enums,
+and decodes an actual preview PNG referenced by executor history.
+
+The upscale GPU/model boundary is mocked to check argument forwarding and
+per-execution helper isolation. Full checkpoint inference, browser canvas
+acceptance and multi-host HTTP transport are not exercised. No HTTP listener,
+workers or model downloads are started; preview files use a temporary scratch
+directory. The test does not install this branch into a live custom-node folder.