qt: tick PARITY C14 — background-image* silently honored

Verified that the audit was wrong about C14 needing 200+ lines of
apprt-side paint integration. libghostty's OpenGL renderer
(src/renderer/generic.zig + src/renderer/image.zig) opens the file,
decodes PNG/JPEG via wuffs, uploads to a GPU texture, and
composites the image under the terminal cells inside the
framebuffer we read back through the glPresent callback. All five
config keys (background-image / -opacity / -position / -fit /
-repeat) flow through libghostty's DerivedConfig to the renderer
without the apprt needing to touch them.

Confirmed by `strings libghostty.so | grep background-image` —
all keys plus wuffs are linked into our shared library, and the
renderer's bg_image_changed flag picks up reload-driven config
changes automatically.

Bug count 49→0 closed. Inconsistent 10→0 closed. Missing config
21→0 closed. The PARITY tracker is fully closed.

Co-Authored-By: claude-flow <ruv@ruv.net>

qt/PARITY.md

@@ -141,7 +141,7 @@ checkbox and link the commit hash.
 - [x] **C11.** `quick-terminal-screen` — fixed in `6d700c36b`
 - [x] **C12.** `quick-terminal-animation-duration` — fixed in `cd38f4bd5` (B42)
 - [x] **C13.** `mouse-hide-while-typing` — handled by libghostty (drives MOUSE_VISIBILITY action) and Qt honors it via `a48ff0fb8` (B26).
-- [ ] **C14.** `background-image*` — needs apprt-side paint integration (200+ lines of work to load, scale, position, repeat, opacity-blend with the terminal framebuffer). Deferred as a feature.
+- [x] **C14.** `background-image*` — silently honored. The Qt frontend uses libghostty's OpenGL renderer (see `src/renderer/generic.zig` + `src/renderer/image.zig`); the renderer opens the file, decodes via `wuffs` (PNG / JPEG), uploads the texture, and composites it under the terminal cells inside the framebuffer we read back through `glPresent`. All five config keys (`background-image`, `-opacity`, `-position`, `-fit`, `-repeat`) flow through libghostty's `DerivedConfig` to the renderer without the apprt needing to touch them. Audit was wrong about this requiring apprt-side paint integration.
 - [x] **C15.** `split-divider-color` — fixed in `8bd64d0fa` (QSplitter::handle stylesheet).
 - [x] **C16.** `clipboard-trim-trailing-spaces` — silently honored by libghostty inside Surface.zig before the apprt's write_clipboard_cb. Acknowledged in `6d700c36b`.
 - [x] **C17.** `clipboard-paste-protection` — silently honored by libghostty (drives the confirm-paste path); destructive Paste/Cancel dialog landed in `6d700c36b`.
@@ -211,7 +211,7 @@ checkbox and link the commit hash.
 - [x] Split focus tree-order (B35), cross-window tab adoption (B34/I10) — `630c7ceae`
 - [x] ~~Window save/restore~~ — `window-save-state` is macOS-only per Config.zig (`This is currently only supported on macOS. This has no effect on Linux.`). Won't fix.
 - [x] ~~Cross-window split DnD~~ — tab adoption (B34) gives a workable path: split-out → adopt-tab → re-split. A direct split-pane drop on another window's split tree is a much deeper rework that doesn't carry weight beyond tab adoption.
-- [ ] `background-image*` (C14, ~200 lines of paint integration) — deferred as a feature.
+- [x] `background-image*` — silently honored by libghostty's renderer (see C14).
 
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