[refactor] v2: use absolute imports (v2.*) everywhere instead of relative

Mechanical conversion of every relative import under v2/ to an absolute v2.* path
(from .x / ..x / ...x -> from v2.<pkg>.x) so imports are unambiguous, grep-able, and
stable when code is copied/moved between entrypoints (VideoGenerator, CLI, server).

Surgical prefix-only rewrite: only the 'from <dots><module>' prefix changed — import
names, parentheses, multi-line formatting, comments, and ordering are byte-for-byte
preserved (no collapsing, no reorder, no unrelated reformatting).

- 471 imports across 125 files; v2/tests/ was already absolute (untouched).
- Validated: all 125 files compile, every 'from v2.* import' target resolves to a real
  module/package, zero relative imports remain (full sweep), CPU mini suite green
  (202 passed, 2 skipped).

v2/program/__init__.py

@@ -1,7 +1,7 @@
 """Program plane — compose a card's loops into a task (design_v3 §13)."""
 from __future__ import annotations
 
-from .specs import (
+from v2.program.specs import (
     ComponentNode,
     Edge,
     EdgeKind,
@@ -13,7 +13,7 @@ from .specs import (
     when_opt,
     when_task,
 )
-from .workflow import (
+from v2.program.workflow import (
     BestOfNWorkflow,
     ParallelWorkflow,
     Workflow,

v2/program/specs.py

@@ -13,7 +13,7 @@ from dataclasses import dataclass, field
 from enum import Enum
 from typing import Any, Callable
 
-from ..request.tasks import TaskType
+from v2.request.tasks import TaskType
 
 
 class ProgramKind(str, Enum):

v2/program/workflow.py

@@ -111,7 +111,7 @@ class ParallelWorkflow(Workflow):
     def run(self, engine: Any, **initial: Any) -> Any:
         if not self.stages:
             raise ValueError(f"workflow {self.workflow_id!r} has no stages")
-        from ..request.artifacts import Output
+        from v2.request.artifacts import Output
         merged: dict[str, Any] = {}
         metrics: dict[str, float] = {}
         rid = self.workflow_id