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

.gitea/workflows/ci.yml

@@ -11,6 +11,10 @@ on:
 env:
   CARGO_TERM_COLOR: always
   RUSTFLAGS: "-D warnings"
+  # sccache caches compilation artifacts within a job so that compiling
+  # both --features server and --features web shares common crate work.
+  RUSTC_WRAPPER: /usr/local/bin/sccache
+  SCCACHE_DIR: /tmp/sccache
 
 # Cancel in-progress runs for the same branch/PR
 concurrency:
@@ -34,7 +38,10 @@ jobs:
           git fetch --depth=1 origin "${GITHUB_SHA}"
           git checkout FETCH_HEAD
       - run: rustup component add rustfmt
+      # Format check does not compile, so sccache is not needed here.
       - run: cargo fmt --check
+        env:
+          RUSTC_WRAPPER: ""
 
   clippy:
     name: Clippy
@@ -48,12 +55,21 @@ jobs:
           git remote add origin "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}.git"
           git fetch --depth=1 origin "${GITHUB_SHA}"
           git checkout FETCH_HEAD
+      - name: Install sccache
+        run: |
+          curl -fsSL https://github.com/mozilla/sccache/releases/download/v0.9.1/sccache-v0.9.1-x86_64-unknown-linux-musl.tar.gz \
+            | tar xz --strip-components=1 -C /usr/local/bin/ sccache-v0.9.1-x86_64-unknown-linux-musl/sccache
+          chmod +x /usr/local/bin/sccache
       - run: rustup component add clippy
-      # Lint both feature sets independently
+      # Lint both feature sets independently.
+      # sccache deduplicates shared crates between the two compilations.
       - name: Clippy (server)
         run: cargo clippy --features server --no-default-features -- -D warnings
       - name: Clippy (web)
         run: cargo clippy --features web --no-default-features -- -D warnings
+      - name: Show sccache stats
+        run: sccache --show-stats
+        if: always()
 
   audit:
     name: Security Audit
@@ -69,7 +85,11 @@ jobs:
           git fetch --depth=1 origin "${GITHUB_SHA}"
           git checkout FETCH_HEAD
       - run: cargo install cargo-audit
+        env:
+          RUSTC_WRAPPER: ""
       - run: cargo audit
+        env:
+          RUSTC_WRAPPER: ""
 
   # ---------------------------------------------------------------------------
   # Stage 2: Tests (only after all quality checks pass)
@@ -87,10 +107,18 @@ jobs:
           git remote add origin "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}.git"
           git fetch --depth=1 origin "${GITHUB_SHA}"
           git checkout FETCH_HEAD
+      - name: Install sccache
+        run: |
+          curl -fsSL https://github.com/mozilla/sccache/releases/download/v0.9.1/sccache-v0.9.1-x86_64-unknown-linux-musl.tar.gz \
+            | tar xz --strip-components=1 -C /usr/local/bin/ sccache-v0.9.1-x86_64-unknown-linux-musl/sccache
+          chmod +x /usr/local/bin/sccache
       - name: Run tests (server)
         run: cargo test --features server --no-default-features
       - name: Run tests (web)
         run: cargo test --features web --no-default-features
+      - name: Show sccache stats
+        run: sccache --show-stats
+        if: always()
 
   # ---------------------------------------------------------------------------
   # Stage 3: Deploy (only after tests pass, only on main)
@@ -108,4 +136,3 @@ jobs:
           apk add --no-cache curl
           curl -sf "${{ secrets.COOLIFY_WEBHOOK }}" \
             -H "Authorization: Bearer ${{ secrets.COOLIFY_TOKEN }}"
-