feat(i18n): add language-pack scaffold with English and Spanish

Introduces ``src/i18n`` with a tiny JSON-backed t() lookup, an in-session
language preference, and a sidebar selector wired through
``hide_streamlit_chrome`` so every page picks up the same picker. Covers
home, tool cards, findings panel, gate, shutdown, and pickup banner
strings. Tests pin pack parity and the farewell-overlay JS escape so
future packs can't silently regress.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/i18n/packs/en.json

@@ -0,0 +1,97 @@
+{
+  "chrome": {
+    "language_label": "Language",
+    "footer": "Runs locally. Your data never leaves this computer. | DataTools v3.0"
+  },
+  "home": {
+    "page_title": "DataTools — Data Cleaning Mastery",
+    "title": "🧹 DataTools — Data Cleaning Mastery",
+    "caption": "A 9-tool suite for cleaning, standardizing, and validating tabular data. Runs 100% locally.",
+    "findings_badge_one": "{n} finding",
+    "findings_badge_other": "{n} findings"
+  },
+  "status": {
+    "ready": "Ready",
+    "coming_soon": "Coming Soon"
+  },
+  "upload": {
+    "heading": "📤 Upload a file to start",
+    "intro": "Optional: scan an uploaded file for data quality issues and see which tools can fix each one. Skip if you already know what you need.",
+    "limits": "**Up to 1 GB.** Formats: CSV, TSV, XLSX, XLS. Delimiters auto-detected: comma, tab, semicolon, pipe. Encodings auto-detected: UTF-8 (with/without BOM), UTF-16, cp1252, Latin-1/9, cp1250, ISO-8859-2, cp1251, KOI8-R, Mac Roman, Shift_JIS, GB18030, Big5, EUC-KR — and override on the Review page.",
+    "uploader_label": "Upload CSV or Excel",
+    "uploader_help": "Up to 1 GB. Comma / tab / semicolon / pipe delimiters all auto-detected. Encoding auto-detected with override on the Review page if needed.",
+    "run_button": "Run analysis",
+    "skip_button": "Skip",
+    "scanning": "Scanning…",
+    "skipped_notice": "Analysis skipped. Open any tool below to start working.",
+    "using_session_file": "Using **{name}** from the upload screen.",
+    "use_different_file": "Use a different file",
+    "switch_back": "Switch back to upload-screen file",
+    "pickup_caption": "Up to 1 GB. Delimiters auto-detected: comma, tab, semicolon, pipe. Encoding auto-detected (UTF-8 / UTF-16 / cp1252 / Latin-1 family / cp1250 / cp1251 / KOI8-R / Mac Roman / Shift_JIS / GB18030 / Big5 / EUC-KR), with override on the Review page."
+  },
+  "findings": {
+    "header": "Detected issues",
+    "none": "No issues detected. Open any tool below to start working.",
+    "severity_summary_segment": "{icon} {n} {severity}",
+    "tool_section_label": "{tool} — {n} finding(s)",
+    "other_section_label": "Other / file-level — {n} finding(s)",
+    "open_tool": "Open {tool} →",
+    "untargeted_label": "Informational"
+  },
+  "gate": {
+    "warning": "**{name}** must pass the CSV-normalization gate before you can use this tool. Open the Review page to apply the fixes our analyzer recommends.",
+    "default_name": "the uploaded file",
+    "open_review": "Go to Review & Normalize"
+  },
+  "quit": {
+    "button": "Quit app",
+    "shutting_down": "Shutting down… you can close this window.",
+    "farewell_title": "DataTools has shut down",
+    "farewell_subtitle": "You can close this window."
+  },
+  "close_page": {
+    "page_title": "DataTools — Close",
+    "title": "🛑 Close DataTools",
+    "caption": "Shut down the local app and free the terminal.",
+    "body": "Clicking the button below will terminate the DataTools server. Any unsaved work in other tools will be lost. Once the app shuts down you can close this window.",
+    "button": "Close the app"
+  },
+  "tools": {
+    "01_deduplicator": {
+      "name": "Deduplicator",
+      "description": "Fuzzy matching, normalization, survivor selection, and interactive review."
+    },
+    "02_text_cleaner": {
+      "name": "Text Cleaner",
+      "description": "Whitespace trim, multi-space collapse, Unicode normalization, BOM and line-ending handling."
+    },
+    "03_format_standardizer": {
+      "name": "Format Standardizer",
+      "description": "Standardize dates, currencies, names, phone numbers, and addresses."
+    },
+    "04_missing_handler": {
+      "name": "Missing Value Handler",
+      "description": "Detect disguised nulls, missingness analysis, and imputation strategies."
+    },
+    "05_column_mapper": {
+      "name": "Column Mapper",
+      "description": "Rename columns, enforce a target schema, and coerce types."
+    },
+    "06_outlier_detector": {
+      "name": "Outlier Detector",
+      "description": "Z-score, IQR, and MAD detection with domain-rule violations and winsorization."
+    },
+    "07_multi_file_merger": {
+      "name": "Multi-File Merger",
+      "description": "Combine multiple CSV/Excel files with schema alignment."
+    },
+    "08_validator_reporter": {
+      "name": "Validator & Reporter",
+      "description": "Validate against rules and generate PDF/Excel quality reports."
+    },
+    "09_pipeline_runner": {
+      "name": "Pipeline Runner",
+      "description": "Chain tools in recommended order and pass output between steps."
+    }
+  }
+}