Move migrations to internal/db/migrations (closes #96)

REPO_POLICIES.md puts migrations in internal/db/migrations/ as
000_migration.sql and 001_schema.sql. The two files move there with
their contents unchanged. go:embed cannot reach outside its own
package, so internal/db/migrations has a small package that embeds
them, and internal/database reads them through its FS(). The database
package stays where CONVENTIONS.md puts it; moving it would change
existing test files in other packages.

The version still comes from the filename prefix, so a database that
has recorded versions 0 and 1 runs neither again. A new test applies
the migrations twice to one database file and checks that the second
run applies nothing.

Model: opus-5-5

internal/database/database.go

@@ -4,9 +4,9 @@ package database
 import (
 	"context"
 	"database/sql"
-	"embed"
 	"errors"
 	"fmt"
+	"io/fs"
 	"log/slog"
 	"path/filepath"
 	"sort"
@@ -15,14 +15,12 @@ import (
 
 	"go.uber.org/fx"
 	"sneak.berlin/go/pixa/internal/config"
+	"sneak.berlin/go/pixa/internal/db/migrations"
 	"sneak.berlin/go/pixa/internal/logger"
 
 	_ "modernc.org/sqlite" // SQLite driver registration
 )
 
-//go:embed schema/*.sql
-var schemaFS embed.FS
-
 // bootstrapVersion is the migration that creates the schema_migrations
 // table itself. It is applied before the normal migration loop.
 const bootstrapVersion = 0
@@ -113,29 +111,29 @@ func New(lc fx.Lifecycle, params Params) (*Database, error) {
 	return s, nil
 }
 
-// collectMigrations reads the embedded schema directory and returns
+// collectMigrations reads the embedded migrations directory and returns
 // migration filenames sorted lexicographically.
 func collectMigrations() ([]string, error) {
-	entries, err := schemaFS.ReadDir("schema")
+	entries, err := fs.ReadDir(migrations.FS(), ".")
 	if err != nil {
-		return nil, fmt.Errorf("failed to read schema directory: %w", err)
+		return nil, fmt.Errorf("failed to read migrations directory: %w", err)
 	}
 
-	var migrations []string
+	var filenames []string
 
 	for _, entry := range entries {
 		if !entry.IsDir() && strings.HasSuffix(entry.Name(), ".sql") {
-			migrations = append(migrations, entry.Name())
+			filenames = append(filenames, entry.Name())
 		}
 	}
 
-	sort.Strings(migrations)
+	sort.Strings(filenames)
 
-	return migrations, nil
+	return filenames, nil
 }
 
 // bootstrapMigrationsTable ensures the schema_migrations table exists
-// by applying 000.sql if the table is missing.
+// by applying 000_migration.sql if the table is missing.
 func bootstrapMigrationsTable(ctx context.Context, db *sql.DB, log *slog.Logger) error {
 	var tableExists int
 
@@ -150,9 +148,9 @@ func bootstrapMigrationsTable(ctx context.Context, db *sql.DB, log *slog.Logger)
 		return nil
 	}
 
-	content, err := schemaFS.ReadFile("schema/000.sql")
+	content, err := fs.ReadFile(migrations.FS(), "000_migration.sql")
 	if err != nil {
-		return fmt.Errorf("failed to read bootstrap migration 000.sql: %w", err)
+		return fmt.Errorf("failed to read bootstrap migration 000_migration.sql: %w", err)
 	}
 
 	if log != nil {
@@ -177,12 +175,12 @@ func ApplyMigrations(ctx context.Context, db *sql.DB, log *slog.Logger) error {
 		return err
 	}
 
-	migrations, err := collectMigrations()
+	filenames, err := collectMigrations()
 	if err != nil {
 		return err
 	}
 
-	for _, migration := range migrations {
+	for _, migration := range filenames {
 		version, parseErr := ParseMigrationVersion(migration)
 		if parseErr != nil {
 			return parseErr
@@ -208,7 +206,7 @@ func ApplyMigrations(ctx context.Context, db *sql.DB, log *slog.Logger) error {
 		}
 
 		// Read and apply migration.
-		content, readErr := schemaFS.ReadFile(filepath.Join("schema", migration))
+		content, readErr := fs.ReadFile(migrations.FS(), migration)
 		if readErr != nil {
 			return fmt.Errorf("failed to read migration %s: %w", migration, readErr)
 		}