Viewer: save to Vita, turn with L/R; album name order, cover shape setting

- Inside an album, SELECT cycles newest / oldest / file name A-Z / Z-A
  (natural, case-insensitive; name orders drop the month headers and
  L/R jump by initial letter). Asset originalFileName is now parsed.
- Full-screen viewer: Triangle or the "Save to Vita" button downloads
  the original (falling back to Immich's full-size / preview JPEG) and
  exports it to the Photos app via ScePhotoExport (new src/export.c).
  The video downloader is now a generic download_to_file().
- R / L turn the whole viewer 90 degrees clockwise / counter-clockwise
  so the Vita can be held upright (new src/viewrot.c): it renders into
  a portrait render target drawn rotated, and maps d-pad, sticks and
  touch into the turned screen. Zoom moves to the right stick only.
  SCREEN_W/H are now variables for that logical screen.
- Server & Backup page: album cover shape setting (vertical 3:4,
  square, panoramic 16:9), saved as covershape= in config.txt.
- Test builds: "rup" holds the right stick up in test_input.txt.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -92,6 +92,18 @@ handheld.
 | △ | Reload the album list |
 | O | Clear the search, then back |
 
+Cover shape — **Vertical** (3:4), **Square** or **Panoramic** (16:9) — is
+picked on the *Server & Backup* page (**L / R** or tap) and saved as
+`covershape=` in `config.txt`.
+
+**Inside an album**
+
+| Button | Action |
+| --- | --- |
+| SELECT | Order: newest → oldest → file name A‑Z → Z‑A (name orders drop the month headers) |
+| L / R | Jump a month (or, sorted by name, an initial letter) |
+| O | Back to the album list |
+
 **Places map**
 
 | Button | Action |
@@ -107,8 +119,10 @@ handheld.
 | Button | Action |
 | --- | --- |
 | ← / → | Previous / next |
-| Right stick / L · R | Zoom · left stick pans |
+| R / L | Turn the viewer 90° clockwise / counter‑clockwise — hold the Vita upright and portrait photos fill the screen (d‑pad, sticks and touch follow the turn) |
+| Right stick | Zoom · left stick pans |
 | X | Play video / retry a failed load |
+| △ (or tap "Save to Vita") | Save the photo to the Vita's Photos app (JPEG/PNG original, else Immich's full-size JPEG) |
 | O | Back |
 
 **Video playback** — X pause/resume · ←/→ seek ±10 s · O stop.