add file storage: metadata schema, minio upload/download, content-type extension mapping

- add files_metadata and files_metadata_connections tables with CRUD helpers
- add FileMetadata type and Sha256Hash typedef; replace Media struct
- add minio upload, presigned download URL, and key generation
- fix bucket existence check to use FileStorageBucketName instead of hardcoded "main"
- fix files_metadata_connections table name and trailing comma in DDL
- fix column name original -> name in files_metadata schema
- add canonical MIME-to-extension map with .unk fallback
- add FileDownloadLinkTtl constant (24h)

packages/types/types.go

@@ -1,6 +1,7 @@
 package types
 
 import (
+	"crypto/sha256"
 	"math/rand/v2"
 	"sync"
 	"time"
@@ -14,6 +15,7 @@ import (
 )
 
 type Rgba [4]uint8
+type Sha256Hash [sha256.Size]byte
 
 func (r Rgba) GetRandom() *Rgba {
 	for i := range r {
@@ -103,8 +105,11 @@ type WsAuthMessage struct {
 	Error   string `json:"error"`
 }
 
-type Media struct {
-	Hash      string
-	Owner     uint32
-	CreatedAt time.Time
+type FileMetadata struct {
+	CreatedAt   time.Time   `json:"createdAt"`
+	Connections []uuid.UUID `json:"connections"`
+	Name        string      `json:"name"`
+	Hash        Sha256Hash  `json:"hash"`
+	Id          uuid.UUID   `json:"id"`
+	UploaderId  uuid.UUID   `json:"uploaderId"`
 }