feat: Enable series name editing with duplicate validation

- Remove disabled state from series name input in edit modal
- Add duplicate name validation in SeriesController (resolves TODO)
- Update nameIgnorePrefix when series name changes
- Add frontend validation for duplicate series names
- Add updateSeriesName method to PATCH series immediately on rename
- Show backend error message in toast on failure
- Add i18n string for duplicate name error message

This enables users to rename existing series while preventing duplicate
series names within the same library.

client/components/modals/EditSeriesInputInnerModal.vue

@@ -8,7 +8,7 @@
         <div class="bg-bg rounded-lg px-2 py-6 sm:p-6 md:p-8" @click.stop>
           <div class="flex">
             <div class="grow p-1 min-w-48 sm:min-w-64 md:min-w-80">
-              <ui-input-dropdown ref="newSeriesSelect" v-model="selectedSeries.name" :items="existingSeriesNames" :disabled="!isNewSeries" :label="$strings.LabelSeriesName" @input="seriesNameInputHandler" />
+              <ui-input-dropdown ref="newSeriesSelect" v-model="selectedSeries.name" :items="existingSeriesNames" :label="$strings.LabelSeriesName" @input="seriesNameInputHandler" />
             </div>
             <div class="w-24 sm:w-28 md:w-40 p-1">
               <ui-text-input-with-label ref="sequenceInput" v-model="selectedSeries.sequence" :label="$strings.LabelSequence" />