fix(codegen): sort map iteration to make generated output deterministic

Table.Columns/Constraints/Indexes/Relationships are Go maps, and every
writer, reader, diff, inspector, and merge code path that iterated them
directly was subject to Go's randomized map order, so identical input
could produce different output (or a different in-report violation/diff
order) on every run. Most visibly this showed up as bun/gorm `unique:`
struct tags changing order across consecutive `make models` runs with no
source change.

Fixed by sorting map iteration (by Sequence then Name, or alphabetically
for string-keyed maps) everywhere the order affects generated output or
first-match tie-break logic, across the bun, gorm, sqlite, dbml, drawdb,
pgsql, prisma, graphql, typeorm, drizzle, and dctx writers; the dctx,
prisma, and typeorm readers; the shared models.GetPrimaryKey/
GetForeignKeys helpers; pkg/diff, pkg/inspector, and pkg/merge; and the
TUI column/relationship pickers in pkg/ui.

pkg/models/models.go

@@ -5,6 +5,7 @@
 package models
 
 import (
+	"sort"
 	"strings"
 	"time"
 
@@ -141,15 +142,28 @@ func (d *Table) SQLName() string {
 
 // GetPrimaryKey returns the primary key column for the table, or nil if none exists.
 func (m Table) GetPrimaryKey() *Column {
+	var pk *Column
 	for _, column := range m.Columns {
-		if column.IsPrimaryKey {
-			return column
+		if !column.IsPrimaryKey {
+			continue
+		}
+		if pk == nil || columnLess(column, pk) {
+			pk = column
 		}
 	}
-	return nil
+	return pk
 }
 
-// GetForeignKeys returns all foreign key constraints for the table.
+// columnLess reports whether a should sort before b, by Sequence then Name.
+func columnLess(a, b *Column) bool {
+	if a.Sequence > 0 && b.Sequence > 0 {
+		return a.Sequence < b.Sequence
+	}
+	return a.Name < b.Name
+}
+
+// GetForeignKeys returns all foreign key constraints for the table, sorted
+// deterministically by Sequence then Name.
 func (m Table) GetForeignKeys() []*Constraint {
 	keys := make([]*Constraint, 0)
 
@@ -158,6 +172,12 @@ func (m Table) GetForeignKeys() []*Constraint {
 			keys = append(keys, c)
 		}
 	}
+	sort.Slice(keys, func(i, j int) bool {
+		if keys[i].Sequence > 0 && keys[j].Sequence > 0 {
+			return keys[i].Sequence < keys[j].Sequence
+		}
+		return keys[i].Name < keys[j].Name
+	})
 	return keys
 }