chore: stop treating dirs as having size 128 (#10750)

Resp. directories for the database, and both dirs and symlinks for
`FileInfo.FileSize`. Instead handle it in the UI progress percentage. We
even already have special cases there for deletions, might as well
handle directories just like any other zero-sized needed item there.

This went through the very thorough testing of running it on my laptop,
the migration was applied and it seemed to be working fine after.

---------

Signed-off-by: Simon Frei <freisim93@gmail.com>

internal/db/sqlite/db_test.go

@@ -29,7 +29,6 @@ import (
 const (
 	folderID  = "test"
 	blockSize = 128 << 10
-	dirSize   = 128
 )
 
 func TestBasics(t *testing.T) {
@@ -72,11 +71,11 @@ func TestBasics(t *testing.T) {
 		t.Fatal(err)
 	}
 	const (
-		localSize      = (1+2+3)*blockSize + dirSize
+		localSize      = (1+2+3)*blockSize
 		remoteSize     = (3 + 4 + 5) * blockSize
-		globalSize     = (2+3+3+4+5)*blockSize + dirSize
+		globalSize     = (2+3+3+4+5)*blockSize
 		needSizeLocal  = remoteSize
-		needSizeRemote = (2+3)*blockSize + dirSize
+		needSizeRemote = (2+3)*blockSize
 	)
 
 	t.Run("SchemaVersion", func(t *testing.T) {

internal/db/sqlite/folderdb_update.go

@@ -111,10 +111,6 @@ func (s *folderDB) Update(device protocol.DeviceID, fs []protocol.FileInfo, opti
 			f.BlocksHash = nil
 		}
 
-		if f.Type == protocol.FileInfoTypeDirectory {
-			f.Size = 128 // synthetic directory size
-		}
-
 		// Insert the file.
 		//
 		// If it is a remote file, set remote_sequence otherwise leave it at

internal/db/sqlite/sql/migrations/folder/06-zero-size-dirs.sql

@@ -0,0 +1,12 @@
+-- Copyright (C) 2026 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+-- All non-file entries should have size zero.
+-- Directories were previously stored with a "synthetic" size of 128.
+UPDATE files
+    SET size = 0
+    WHERE type != 0
+;

internal/db/sqlite/util.go

@@ -106,6 +106,10 @@ func (i indirectFI) FileInfo() (protocol.FileInfo, error) {
 		fi.Blocks = bl.Blocks
 	}
 	fi.Name = osutil.NativeFilename(fi.Name)
+	// Undo earlier behaviour of setting a synthetic size on dirs.
+	if fi.Type != protocol.FileInfoTypeFile && fi.Size > 0 {
+		fi.Size = 0
+	}
 	return protocol.FileInfoFromDB(&fi), nil
 }