fix(import): replace import removes the previous site media

[DavidBabinec]

The bug

A replace import wiped rows, folders and redirects but kept the previous site's media_assets rows. Importing a second site that ships a file at the same storage path, such as two sites that embed the same font file, failed with UNIQUE constraint failed: media_assets.public_path after the data had committed, and the new bytes had already overwritten the old asset's file.

The fix

replace now deletes the media library inside the import transaction and removes the files after commit, before the bundle's media is written. It does this only when the import carries both media and the site shell, runs on main, and no other branch exists; user avatars and plugin-managed media are kept. The archive endpoint now calls the JSON endpoint's apply path directly, and the custom-table delete binds its boolean so replace runs on Postgres.

Verification

src/__tests__/server/importReplaceMedia.test.ts fails on main (4 of 10) and passes here on SQLite and on a local Postgres 16.

before: {"error":"UNIQUE constraint failed: media_assets.public_path"}
after:  10 pass, 0 fail
BUILD_EXIT=0 LINT_EXIT=0 TEST_EXIT=0 (7132 pass, 0 fail)