Add Phase 4: code quality, CI/CD, and formatting

- testthat infrastructure with 15 tests covering env-var guards,
  return types for all format/save functions, and spelling
- inst/WORDLIST with 52 domain terms (LightGBM, MinIO, Parquet, etc.)
- Spelling test wired into devtools::test() via test-spelling.R
- styler::style_file() added as step 0 in deploy.R (auto-fixes before ship)
- .gitea/workflows/test.yaml: runs testthat suite on push
- .gitea/workflows/lint.yaml: lychee link check + styler dry-run on push
- Removed internal IP address from comment in train_production_model()
- Language: en-US added to DESCRIPTION

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

.gitea/workflows/test.yaml

@@ -0,0 +1,31 @@
+name: R Package Tests
+
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+    branches: [main, master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    container:
+      image: rocker/tidyverse:4.4
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install system dependencies
+        run: |
+          apt-get update -y
+          apt-get install -y libcurl4-openssl-dev libssl-dev libxml2-dev
+
+      - name: Install R package dependencies
+        run: |
+          Rscript -e "install.packages(c('remotes', 'testthat', 'withr'))"
+          Rscript -e "remotes::install_deps(dependencies = TRUE)"
+
+      - name: Run tests
+        run: |
+          Rscript -e "devtools::test()"