* fix(images): preserve Windows preview paths
Provider image markdown used escaped backslash paths on Windows, which markdown parsing could turn into encoded drive paths that the app treated as workspace-relative. Emit drive-letter paths as file URIs and normalize existing encoded local paths before file preview.
* test(server): accept file URI image sources
Windows provider image output now renders drive-letter paths as file URIs. Decode those markdown sources before filesystem assertions so the image rendering tests keep checking the materialized file.
* fix(images): keep plain local paths literal
Limit legacy URI decoding to markdown-encoded Windows drive paths so ordinary local paths with percent sequences remain unchanged. Document why provider image markdown matching still accepts old doubled-backslash history.
