feat(i18n): add internationalization with DE, FR, ES, PT translations (#12)

Add a compile-time i18n system with 270 translation keys across 5 locales
(EN, DE, FR, ES, PT). Translations are embedded via include_str! and parsed
lazily into flat HashMaps with English fallback for missing keys.

- Add src/i18n module with Locale enum, t()/tw() lookup functions, and tests
- Add JSON translation files for all 5 locales under assets/i18n/
- Provide locale Signal via Dioxus context in App, persisted to localStorage
- Replace all hardcoded UI strings across 33 component/page files
- Add compact locale picker (globe icon + ISO alpha-2 code) in sidebar header
- Add click-outside backdrop dismissal for locale dropdown

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Co-authored-by: Sharang Parnerkar <parnerkarsharang@gmail.com>
Reviewed-on: #12

assets/tailwind.css

@@ -356,6 +356,95 @@
       }
     }
   }
+  .dropdown {
+    @layer daisyui.l1.l2.l3 {
+      position: relative;
+      display: inline-block;
+      position-area: var(--anchor-v, bottom) var(--anchor-h, span-right);
+      & > *:not(:has(~ [class*="dropdown-content"])):focus {
+        --tw-outline-style: none;
+        outline-style: none;
+        @media (forced-colors: active) {
+          outline: 2px solid transparent;
+          outline-offset: 2px;
+        }
+      }
+      .dropdown-content {
+        position: absolute;
+      }
+      &.dropdown-close .dropdown-content, &:not(details, .dropdown-open, .dropdown-hover:hover, :focus-within) .dropdown-content, &.dropdown-hover:not(:hover) [tabindex]:first-child:focus:not(:focus-visible) ~ .dropdown-content {
+        display: none;
+        transform-origin: top;
+        opacity: 0%;
+        scale: 95%;
+      }
+      &[popover], .dropdown-content {
+        z-index: 999;
+        @media (prefers-reduced-motion: no-preference) {
+          animation: dropdown 0.2s;
+          transition-property: opacity, scale, display;
+          transition-behavior: allow-discrete;
+          transition-duration: 0.2s;
+          transition-timing-function: cubic-bezier(0.4, 0, 0.2, 1);
+        }
+      }
+      @starting-style {
+        &[popover], .dropdown-content {
+          scale: 95%;
+          opacity: 0;
+        }
+      }
+      &:not(.dropdown-close) {
+        &.dropdown-open, &:not(.dropdown-hover):focus, &:focus-within {
+          > [tabindex]:first-child {
+            pointer-events: none;
+          }
+          .dropdown-content {
+            opacity: 100%;
+            scale: 100%;
+          }
+        }
+        &.dropdown-hover:hover {
+          .dropdown-content {
+            opacity: 100%;
+            scale: 100%;
+          }
+        }
+      }
+      &:is(details) {
+        summary {
+          &::-webkit-details-marker {
+            display: none;
+          }
+        }
+      }
+      &:where([popover]) {
+        background: #0000;
+      }
+      &[popover] {
+        position: fixed;
+        color: inherit;
+        @supports not (position-area: bottom) {
+          margin: auto;
+          &.dropdown-close, &.dropdown-open:not(:popover-open) {
+            display: none;
+            transform-origin: top;
+            opacity: 0%;
+            scale: 95%;
+          }
+          &::backdrop {
+            background-color: color-mix(in oklab, #000 30%, #0000);
+          }
+        }
+        &.dropdown-close, &:not(.dropdown-open, :popover-open) {
+          display: none;
+          transform-origin: top;
+          opacity: 0%;
+          scale: 95%;
+        }
+      }
+    }
+  }
   .btn {
     :where(&) {
       @layer daisyui.l1.l2.l3 {