Refresh the C2PA soft-binding snapshot and fix Ruff ICN001

The upstream registry gained be.immostory.videoseal.1 at revision d5960248,
so `sync_c2pa_soft_bindings.py --check` failed lint on main and on every pull
request. That step runs ahead of Ruff, which hid an ICN001 error in
scripts/_corpus_scan.py; import `date` directly, as the sibling scripts do.
Document the check's live-upstream behavior next to the refresh command.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/_corpus_scan.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-import datetime
+from datetime import date
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
@@ -10,15 +10,15 @@ if TYPE_CHECKING:
     from pathlib import Path
 
 
-def corpus_day(path: Path, corpus: Path) -> datetime.date | None:
+def corpus_day(path: Path, corpus: Path) -> date | None:
     """Read the leading YYYY-MM-DD corpus segment, if present."""
     try:
-        return datetime.date.fromisoformat(path.relative_to(corpus).parts[0])
+        return date.fromisoformat(path.relative_to(corpus).parts[0])
     except (ValueError, IndexError):
         return None
 
 
-def corpus_files(corpus: Path, since: datetime.date | None, *, suffixes: Collection[str] | None = None) -> list[Path]:
+def corpus_files(corpus: Path, since: date | None, *, suffixes: Collection[str] | None = None) -> list[Path]:
     """Return a deterministic recursive walk, optionally date- and suffix-bounded."""
     if since is None:
         candidates = corpus.rglob("*")