feat(modes): Mode dataclass + empty MODE_REGISTRY skeleton

modes.py

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+"""MODE_REGISTRY — one Mode entry per generation mode.
+
+Each Mode declares:
+- name: short id ("t2v", "i2v", ...)
+- label: display name
+- icon: single-character or emoji icon for the sidebar
+- stage_map: list of (label, expected_share_pct) for the status banner
+- parameterize_fn: (Gradio inputs dict) -> list[(node_id, widget_index, value)]
+
+The parameterize_fn is the only mode-specific logic. Everything else (workflow
+loading, validation, dispatch) is mode-agnostic and lives in workflow.py /
+backend.py.
+
+Tasks 11 (T2V + I2V) and 12 (A2V + Lipsync + Keyframe + Style) populate
+MODE_REGISTRY. This task only sets up the dataclass and the empty container.
+"""
+from __future__ import annotations
+
+from collections.abc import Callable
+from dataclasses import dataclass, field
+from typing import Any
+
+Patch = tuple[int, int, Any]
+ParameterizeFn = Callable[[dict[str, Any]], list[Patch]]
+
+
+@dataclass(frozen=True)
+class Stage:
+    label: str
+    share_pct: int  # rough share of total time, sums to ~100 across stages
+
+
+@dataclass(frozen=True)
+class Mode:
+    name: str
+    label: str
+    icon: str
+    parameterize_fn: ParameterizeFn
+    stage_map: list[Stage] = field(default_factory=list)
+
+
+# Filled in by tasks 11–12.
+MODE_REGISTRY: dict[str, Mode] = {}

tests/test_modes.py

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+"""Unit tests for modes.py — MODE_REGISTRY and parameterize_fn correctness."""
+import pytest
+
+import modes
+
+
+def test_mode_dataclass_has_expected_fields():
+    """Mode dataclass exposes the expected attribute set."""
+    fields = {"name", "label", "icon", "parameterize_fn", "stage_map"}
+    actual = set(modes.Mode.__dataclass_fields__.keys())
+    assert fields == actual
+
+
+def test_mode_registry_is_a_dict():
+    """MODE_REGISTRY exists and is a dict (entries added in Tasks 11–12)."""
+    assert isinstance(modes.MODE_REGISTRY, dict)