fix: escape enum values as Go string literals in generated code (#4448)

[ArdyJunata]

Summary

Fixes #4448

Problem

Enum values were interpolated raw into the Go code generation template:

{{.Name}} {{.Type}} = "{{.Value}}"

This causes silent data corruption for any PostgreSQL enum value containing special characters:

DB Enum Value	Generated Go Constant	Bug
user\nadmin (backslash + n, 11 bytes)	"user\nadmin" (newline, 10 bytes)	Silent mismatch — comparisons always fail
say "hello"	"say "hello""	Breaks go/format.Source() entirely
injected" + "arbitrary"	"injected" + "arbitrary"	Compiles as Go string concatenation with wrong value

Fix

Replace "{{.Value}}" with {{printf "%q" .Value}} on line 95 of template.tmpl.

Go's %q verb produces a properly double-quoted, fully-escaped string literal — backslashes are doubled, double quotes are escaped, control characters use named sequences. The outer quotes are included by %q, so no surrounding quotes are needed in the template.

Before:

UserRoleUsernadmin UserRole = "user\nadmin"  // \n = newline! (10 bytes)

After:

UserRoleUsernadmin UserRole = "user\\nadmin"  // correct (11 bytes, matches DB)

Testing

Regression tests added in internal/codegen/golang/enum_test.go covering:

• Plain values (unchanged)
• Literal backslash sequences (\n, \t, \\)
• Embedded control characters (actual newline, tab)
• Double quotes embedded in values
• String concatenation injection pattern

All 13 new sub-tests pass.