fix(api): use varchar(64) instead of char(64) in GORM models to prevent unnecessary ALTER TABLE on every pod startup (#461)

PostgreSQL stores char(64) as bpchar internally. GORM AutoMigrate compares
the model type "char(64)" against the database type "bpchar" and sees a
mismatch, issuing ALTER TABLE ... ALTER COLUMN TYPE char(64) on every pod
restart. This ALTER acquires an ACCESS EXCLUSIVE lock, blocking all
reads/writes and causing cascading connection pool exhaustion under load.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: GenerQAQ

src/server/api/go/internal/modules/model/asset_reference.go

@@ -23,7 +23,7 @@ type AssetReference struct {
 
 	// SHA256 hash as unique identifier for content-based deduplication
 	// Combined with ProjectID as composite unique key
-	SHA256 string `gorm:"type:char(64);not null;uniqueIndex:idx_project_sha256,priority:2" json:"sha256"`
+	SHA256 string `gorm:"type:varchar(64);not null;uniqueIndex:idx_project_sha256,priority:2" json:"sha256"`
 
 	// Canonical S3 key - the first uploaded location or preferred location
 	// When same content is uploaded multiple times within a project, we keep only one copy

src/server/api/go/internal/modules/model/project.go

@@ -9,7 +9,7 @@ import (
 
 type Project struct {
 	ID               uuid.UUID         `gorm:"type:uuid;default:gen_random_uuid();primaryKey" json:"id"`
-	SecretKeyHMAC    string            `gorm:"type:char(64);uniqueIndex;not null" json:"-"`
+	SecretKeyHMAC    string            `gorm:"type:varchar(64);uniqueIndex;not null" json:"-"`
 	SecretKeyHashPHC string            `gorm:"type:varchar(255);not null" json:"-"`
 	Configs          datatypes.JSONMap `gorm:"type:jsonb;index:idx_projects_configs,type:gin" swaggertype:"object" json:"configs"`