fix(store): truncating an append-only log goes through a write handle on Windows (P11c)

std's append(true) opens without FILE_WRITE_DATA, so SetEndOfFile on that
handle is refused (PermissionDenied) on Windows: the torn-line cut on open
(chain::tests::an_unfinished_last_line_is_cut_away_on_open) and the
roll-back of a failed append (chain and journal) could not truncate. Not a
rename/share-delete problem: std already opens with all three sharing
flags. chain::truncate cuts through a short-lived write handle on Windows
and the handle itself elsewhere; the journal's roll-back uses it too.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

crates/ledger-store/src/journal.rs

@@ -228,8 +228,7 @@ impl JournalWriter {
             .and_then(|()| self.file.write_all(b"\n"))
             .and_then(|()| self.file.sync_all());
         if let Err(e) = written {
-            let _ = self.file.set_len(before);
-            let _ = self.file.sync_all();
+            let _ = crate::chain::truncate(&self.file, &self.path, before);
             return Err(e.into());
         }
         self.prev_hash = sha256_hex(bytes.as_bytes());