feat(dbml): @postgres/@sqlite dialect directives (#19)

Add parseable `@<namespace>[(<target>)]: <args>` directives embedded in DBML.
They are stored losslessly on each object's Metadata, round-trip unchanged
through the DBML writer, and are translated to SQL only by the writer for the
matching dialect.

- models: Directive type + catalog; Metadata map added to Column and Index
- dbml reader: parse and attach directives at database/table/column/index
  level; line-numbered errors; repeatable by default with singleton duplicate
  detection. Fixes a preexisting bug where an `indexes {}` closing brace ended
  the table early, dropping trailing Note: and directive lines.
- dbml writer: re-emit directives at their location; idempotent output
- pgsql writer: PARTITION BY / INHERITS / WITH / TABLESPACE (table),
  STORAGE / COMPRESSION / identity (column), WITH / TABLESPACE (index)
- sqlite writer: WITHOUT ROWID / STRICT (table), COLLATE (column)
- --strict-directives flag on ReaderOptions and WriterOptions
- docs/DBML_DIRECTIVES.md + reader/writer READMEs

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ss2MY5J11cRGwEz86ZXk7d

pkg/writers/pgsql/directives_test.go

@@ -0,0 +1,107 @@
+package pgsql
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"git.warky.dev/wdevs/relspecgo/pkg/models"
+	"git.warky.dev/wdevs/relspecgo/pkg/writers"
+)
+
+func directiveTestDB(t *testing.T) *models.Database {
+	t.Helper()
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+	table := models.InitTable("events", "public")
+
+	id := models.InitColumn("id", "events", "public")
+	id.Type = "bigint"
+	id.IsPrimaryKey = true
+	id.NotNull = true
+	models.AddDirective(id.Metadata, models.Directive{Namespace: "postgres", Args: "identity always"})
+	models.AddDirective(id.Metadata, models.Directive{Namespace: "sqlite", Args: "collate NOCASE"})
+	table.Columns["id"] = id
+
+	created := models.InitColumn("created_at", "events", "public")
+	created.Type = "timestamp"
+	created.NotNull = true
+	table.Columns["created_at"] = created
+
+	models.AddDirective(table.Metadata, models.Directive{Namespace: "postgres", Args: "partition by RANGE (created_at)"})
+	models.AddDirective(table.Metadata, models.Directive{Namespace: "postgres", Args: "tablespace fast_data"})
+	models.AddDirective(table.Metadata, models.Directive{Namespace: "sqlite", Args: "without rowid"})
+
+	idx := models.InitIndex("idx_events_created", "events", "public")
+	idx.Columns = []string{"created_at"}
+	models.AddDirective(idx.Metadata, models.Directive{Namespace: "postgres", Args: "with (fillfactor=90)"})
+	models.AddDirective(idx.Metadata, models.Directive{Namespace: "postgres", Args: "tablespace idx_space"})
+	table.Indexes["idx_events_created"] = idx
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+	return db
+}
+
+func TestPgDirectives_WriteDatabasePath(t *testing.T) {
+	var buf bytes.Buffer
+	w := NewWriter(&writers.WriterOptions{})
+	w.writer = &buf
+	if err := w.WriteDatabase(directiveTestDB(t)); err != nil {
+		t.Fatalf("WriteDatabase: %v", err)
+	}
+	out := buf.String()
+
+	for _, want := range []string{
+		") PARTITION BY RANGE (created_at) TABLESPACE fast_data",
+		"GENERATED ALWAYS AS IDENTITY",
+		"WITH (fillfactor=90) TABLESPACE idx_space",
+	} {
+		if !strings.Contains(out, want) {
+			t.Errorf("missing %q in:\n%s", want, out)
+		}
+	}
+	// sqlite directives must never reach PG output.
+	if strings.Contains(out, "WITHOUT ROWID") || strings.Contains(strings.ToUpper(out), "COLLATE NOCASE") {
+		t.Errorf("sqlite directive leaked into PG output:\n%s", out)
+	}
+}
+
+func TestPgDirectives_WriteSchemaPath(t *testing.T) {
+	var buf bytes.Buffer
+	w := NewWriter(&writers.WriterOptions{})
+	w.writer = &buf
+	if err := w.WriteSchema(directiveTestDB(t).Schemas[0]); err != nil {
+		t.Fatalf("WriteSchema: %v", err)
+	}
+	out := buf.String()
+	if !strings.Contains(out, ") PARTITION BY RANGE (created_at) TABLESPACE fast_data;") {
+		t.Errorf("table suffix missing from WriteSchema path:\n%s", out)
+	}
+	if !strings.Contains(out, "WITH (fillfactor=90) TABLESPACE idx_space") {
+		t.Errorf("index clauses missing from WriteSchema path:\n%s", out)
+	}
+}
+
+func TestPgDirectives_StrictUnknownKeyErrors(t *testing.T) {
+	db := directiveTestDB(t)
+	models.AddDirective(db.Schemas[0].Tables[0].Metadata, models.Directive{Namespace: "postgres", Args: "frobnicate x"})
+
+	var buf bytes.Buffer
+	w := NewWriter(&writers.WriterOptions{StrictDirectives: true})
+	w.writer = &buf
+	err := w.WriteSchema(db.Schemas[0])
+	if err == nil || !strings.Contains(err.Error(), "frobnicate") {
+		t.Fatalf("want strict error for unknown postgres key, got %v", err)
+	}
+}
+
+func TestPgDirectives_StrictIgnoresOtherNamespaces(t *testing.T) {
+	// sqlite directives are present but must not trip PG strict mode.
+	var buf bytes.Buffer
+	w := NewWriter(&writers.WriterOptions{StrictDirectives: true})
+	w.writer = &buf
+	if err := w.WriteSchema(directiveTestDB(t).Schemas[0]); err != nil {
+		t.Fatalf("strict mode should ignore non-postgres directives, got %v", err)
+	}
+}