chore(release): prepare v0.16.0

Stable minor since v0.15.0. Bumps version to 0.16.0 across app, web, AUR, and Flatpak AppStream, and refreshes docs, changelog, and SECURITY.

Tag v0.16.0 after this lands on main.

.github/workflows/nightly.yml

@@ -54,7 +54,9 @@ jobs:
             ninja-build \
             build-essential \
             libvulkan-dev \
-            glslc
+            glslc \
+            spirv-headers \
+            spirv-tools
 
       - name: Install build dependencies
         run: |
@@ -310,7 +312,9 @@ jobs:
             ninja-build \
             build-essential \
             libvulkan-dev \
-            glslc
+            glslc \
+            spirv-headers \
+            spirv-tools
 
       - name: Install build dependencies
         run: |

.github/workflows/release.yml

@@ -54,7 +54,9 @@ jobs:
             ninja-build \
             build-essential \
             libvulkan-dev \
-            glslc
+            glslc \
+            spirv-headers \
+            spirv-tools
 
       - name: Install build dependencies
         run: |
@@ -189,7 +191,9 @@ jobs:
             ninja-build \
             build-essential \
             libvulkan-dev \
-            glslc
+            glslc \
+            spirv-headers \
+            spirv-tools
 
       - name: Install build dependencies
         run: |

.github/workflows/unified-pipeline.yml

@@ -218,7 +218,9 @@ jobs:
             ninja-build \
             build-essential \
             libvulkan-dev \
-            glslc
+            glslc \
+            spirv-headers \
+            spirv-tools
 
       - name: Install GObject introspection dependencies
         run: |