fix(sqlite): emit inline foreign keys, bare-name default schema, direct exec

SQLite can't ALTER TABLE ADD CONSTRAINT, so foreign keys are now written
as inline FOREIGN KEY clauses in CREATE TABLE instead of commented-out
ALTER statements. The default schema (public/main) now produces bare
table names instead of a "public_" prefix; other schemas are still
prefixed to avoid collisions. Also adds direct-to-file execution: the
sqlite writer can now apply generated DDL straight to a .db file via
Metadata["connection_string"], wired into `relspec merge --output-conn`.

pkg/writers/sqlite/templates/create_table.tmpl

@@ -6,4 +6,7 @@ CREATE TABLE {{quote_ident (qualified_table_name .Schema .Name)}} (
 {{- if and .PrimaryKey (not $hasAutoIncrement)}}{{if gt (len .Columns) 0}},{{end}}
     PRIMARY KEY ({{range $i, $colName := .PrimaryKey.Columns}}{{if $i}}, {{end}}{{quote_ident $colName}}{{end}})
 {{- end}}
+{{- range .ForeignKeys}},
+    FOREIGN KEY ({{range $i, $col := .Columns}}{{if $i}}, {{end}}{{quote_ident $col}}{{end}}) REFERENCES {{quote_ident (qualified_table_name .ForeignSchema .ForeignTable)}} ({{range $i, $col := .ForeignColumns}}{{if $i}}, {{end}}{{quote_ident $col}}{{end}}){{if .OnDelete}} ON DELETE {{.OnDelete}}{{end}}{{if .OnUpdate}} ON UPDATE {{.OnUpdate}}{{end}}
+{{- end}}
 );