Add custom theming (#2081)

Adds support for user-created custom themes. Custom theme interface is
tucked into the global settings in a non-invasive manner to avoid major
design changes. Builds on the theme structure established by the dark
theme update.

<img width="1486" height="953" alt="image"
src="https://github.com/user-attachments/assets/716bcfc7-af74-41dc-b14a-cfc2f2d2caa9"
/>

<img width="1486" height="956" alt="image"
src="https://github.com/user-attachments/assets/a00f9620-0b1d-4f67-b010-e94dda5dc212"
/>



Here's a few examples of what teams could do, using a few color schemes
from local teams. Imagine the possibilities!

<img width="1485" height="951" alt="image"
src="https://github.com/user-attachments/assets/c3da37b8-f6be-4152-81e0-533297f517fc"
/>

<img width="1483" height="951" alt="image"
src="https://github.com/user-attachments/assets/0d453f7a-cf6f-4c27-97db-603b54c1f73e"
/>

<img width="1485" height="952" alt="image"
src="https://github.com/user-attachments/assets/bf8c7770-e60d-4875-9580-ed7e54e089f4"
/>

<img width="1484" height="952" alt="image"
src="https://github.com/user-attachments/assets/326d89e6-dd6e-4e05-a9fa-c9fc6f880847"
/>

<img width="1482" height="951" alt="image"
src="https://github.com/user-attachments/assets/eb5a2a5d-c103-482c-a62a-5ccd5ba21cc5"
/>

<img width="1482" height="950" alt="image"
src="https://github.com/user-attachments/assets/4831ca56-f322-4345-97af-8963ae8539b1"
/>



Looking for high contrast? Just moments away:
<img width="1484" height="949" alt="image"
src="https://github.com/user-attachments/assets/7ffc65c6-7000-4566-b4f0-c8247f75fb3d"
/>

photon-client/src/components/cameras/CamerasView.vue

@@ -90,14 +90,7 @@ const fpsTooLow = computed<boolean>(() => {
       </div>
     </v-card-text>
     <v-card-text class="pt-0">
-      <v-btn-toggle
-        v-model="value"
-        :multiple="true"
-        mandatory
-        class="fill"
-        style="width: 100%"
-        base-color="surface-variant"
-      >
+      <v-btn-toggle v-model="value" :multiple="true" mandatory class="fill" style="width: 100%">
         <v-btn
           color="buttonPassive"
           class="fill"