Run the local index in WAL mode with a busy timeout (closes #217)

The connection settings were passed as `_journal_mode=`-style
parameters, which the SQLite driver drops without an error, so the
index ran in rollback-journal mode with no busy timeout. `snapshot
list` or `info` reading during a backup could make the backup's next
write fail with "database is locked". Both open paths now pass
`_pragma=` parameters; foreign keys moved there too.

With WAL on, rows committed to the open index can still be in the
-wal file, which a copy of the main file misses. The metadata export
now copies the index with VACUUM INTO, into an empty 0600 file.

The retry after a failed open no longer claims a TRUNCATE recovery; it
retries with the same settings.

Model: opus-5-5

TODO.md

@@ -22,6 +22,15 @@ the tag exists and is exercised; what is left is merging `next` to
 
 # Completed Steps
 
+- 2026-10-06: Made the local index actually run in WAL mode with a busy
+  timeout ([issue #217](https://git.eeqj.de/sneak/vaultik/issues/217)).
+  The connection settings were written in a form the SQLite driver
+  ignores, so the index ran without either and `snapshot list` or `info`
+  during a backup could make the backup's next write fail with
+  `database is locked`. They are now `_pragma=` parameters, and the
+  metadata export copies the open index with `VACUUM INTO`, because a
+  copy of the file alone misses rows still in the `-wal` file.
+
 - 2026-10-06: Made a backup record the real uid and gid of files,
   directories and symlinks
   ([issue #216](https://git.eeqj.de/sneak/vaultik/issues/216)). The