Escape the database path in the SQLite connection string (closes #518)

SQLite reads a file: URI's path only up to the first ? or #, and
decodes %XX escapes in it. With a data directory such as
/srv/hooks#1, every database opened the one file /srv/hooks. The
connection string is now built with url.URL, which escapes the path,
and OmitHost keeps a relative path relative.

Tests open databases in a directory whose name holds #, ? and %, and
at a relative path, and check through PRAGMA database_list that each
opened the file asked for. A handlers test comment that blamed # in
the temporary directory's path is dropped, as that is no longer true.

Model: opus-5-5

internal/database/sqlite_open.go

@@ -242,7 +242,19 @@ func SQLiteDSN(path, mode string) string {
 	)
 	q.Add("_pragma", "journal_mode(WAL)")
 
-	return "file:" + path + "?" + q.Encode()
+	// SQLite reads a file: URI's path only up to the first ? or #, and
+	// decodes %XX escapes in it, so url.URL escapes the path. OmitHost
+	// keeps a relative path as "file:data/x.db"; written
+	// "file://data/x.db", SQLite would reject "data" as the URI's
+	// authority.
+	dsn := url.URL{
+		Scheme:   "file",
+		Path:     path,
+		OmitHost: true,
+		RawQuery: q.Encode(),
+	}
+
+	return dsn.String()
 }
 
 // OpenSQLite opens the SQLite file at path with the service's