[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/models/unified/program.py

@@ -10,10 +10,10 @@ profiles — the §10 "train ≡ serve through one loop" invariant, now spanning
 """
 from __future__ import annotations
 
-from ...program import ComponentNode, ModelLoopNode, Program, ProgramKind
-from ..common import text_encode_node_fn
-from ..omni import vae_decode_node
-from .card import N_REFINE_ACTIONS
+from v2.program import ComponentNode, ModelLoopNode, Program, ProgramKind
+from v2.models.common import text_encode_node_fn
+from v2.models.omni import vae_decode_node
+from v2.models.unified.card import N_REFINE_ACTIONS
 
 
 def apply_refinement_node(refine_slot: str, n_actions: int = N_REFINE_ACTIONS):