Merge: answer Android's memory warnings, and stop reporting a lost root as an empty library

FR-PLAT-AND-5 in full, FR-PLAT-AND-2 in part -- the recovery is built and
live for Nextcloud roots, the SAF cause it names does not exist yet.

FR-PLAT-AND-4 and FR-PLAT-AND-6 are not here, both blocked behind the
same gap: assemble-apk.sh compiles no Java, so the APK cannot carry a
Service or a FileProvider. The container has JDK 17 and build-tools 36;
the build step is what is missing.

Verified: fmt, clippy --workspace --all-targets -D warnings, and 1043
tests across dr-catalog, dr-sync, dr-sync-folder, dr-sync-nextcloud,
dr-plat and dr-ui. The aarch64 target was checked before the branch was
finished but not after; no device was available.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/dr-ui/src/develop.rs

@@ -3066,6 +3066,33 @@ impl DevelopSession {
         Ok((image, rw, rh))
     }
 
+    /// TRACES: FR-PLAT-AND-5 | NFR-RES-1
+    /// Give back the GPU memory this session is holding only to be fast.
+    ///
+    /// The edit is untouched: the graph and its history are CPU-side by
+    /// design (ARCH §6.1), so the photograph, the undo stack and the viewport
+    /// all survive and the next frame simply costs what the first one did.
+    ///
+    /// # What is not released, and what it is waiting on
+    ///
+    /// The demosaiced source is the largest single allocation a session holds
+    /// — a 24 MP frame is about 190 MB of `Rgba16Float` — and it is
+    /// deliberately kept. Dropping it would need the session to be able to
+    /// rebuild itself from the file, and rebuilding a session from a durable
+    /// record is FR-PLAT-AND-3, which is not built. Freeing it now would not
+    /// be an eviction; it would be closing the photograph without telling
+    /// anyone. Likewise the subject distance fields and the segmentation map:
+    /// each is guarded by a key recording what it was built from, and freeing
+    /// one without invalidating its key is the failure `AdjustPass` documents
+    /// under `colour_key`.
+    ///
+    /// So this is the part of the GPU tier that can be given back and asked
+    /// for again with no other machinery, which is exactly as far as an
+    /// eviction should go.
+    pub fn release_gpu_caches(&mut self) {
+        self.adjust.release_caches();
+    }
+
     /// The displayed size, for sizing the viewport.
     ///
     /// The *framed* size, not the sensor's: cropping and quarter turns change