Portable mode: a portable.txt beside the executable keeps the settings in VectorCraftData (#1366)

docs/control-protocol.md

@@ -11,6 +11,8 @@ Set `VECTORCRAFT_CONFIG_DIR` to a dedicated directory for an isolated native tes
 logs, recovery and user libraries then use that root, without importing the legacy DrawCraft profile.
 An unset override preserves the usual platform paths and legacy migration; an explicitly empty override
 disables those paths. `VECTORCRAFT_NO_PREFS` continues to disable preference reads and writes.
+Without the override, a `portable.txt` or `VectorCraft.portable` file beside the executable (as in the
+Windows portable zip) puts that root in `VectorCraftData` next to the executable.
 
 **Only requests are read.** Every line must be a JSON object with a string `method` (`id` and `params`
 are optional; blank lines are skipped). Anything else gets one error reply

docs/releasing.md

@@ -113,6 +113,13 @@ to the target triple, so host build scripts aren't affected.
 - Before packaging, the script checks each binary's PE machine type against `-Arch` (an x64 build
   can never ship labelled arm64), that `vectorcraft.exe` is a GUI program (no console window) and
   that `vectorcraft-cli.exe` is a console program.
+- **Portable zip:** it ships `packaging/windows/portable.txt` beside `vectorcraft.exe`. That
+  marker (or a `VectorCraft.portable` file) switches on portable mode, as in PhotoCraft: `ui.json`
+  and the folders next to it (Swatches, Graphic Styles, Fonts, Data Recovery, logs…) go to
+  `VectorCraftData\` next to the exe instead of `%APPDATA%\VectorCraft`. If that folder isn't
+  writable the app logs a warning and uses `%APPDATA%`. The MSI has no marker.
+  `VECTORCRAFT_CONFIG_DIR` still wins. The logic is in `apps/vectorcraft/src/profile.rs` and works
+  the same on macOS and Linux.
 - `vectorcraft.wxs` (WiX) is a per-machine install into Program Files with a Start Menu shortcut
   and an App Paths entry (Win+R `vectorcraft`). Same-version upgrades are allowed, so release
   candidates replace each other.