feat: 3 new tools, format streaming, distribution-ready demo + landing pages

Tools shipped this batch (4 → 6 of 9 Ready):
  04 Missing Value Handler   src/core/missing.py + cli_missing.py + GUI
  05 Column Mapper           src/core/column_mapper.py + cli_column_map.py + GUI
  09 Pipeline Runner         src/core/pipeline.py + cli_pipeline.py + GUI
                             with soft tool-dependency graph (recommended,
                             not enforced) and JSON save/load for repeatable
                             weekly cleanups.

Format Standardizer reworked for 1 GB international files:
  • Vectorised dispatch + LRU cache over phone/date/currency/boolean/email
  • Per-row country / address columns drive parsing
  • Audit cap (default 10 k rows, ~50 MB RAM)
  • standardize_file(): chunked streaming entry point (~165 k rows/sec)
  • currency_decimal="auto" for EU comma-decimal locales
  • R$ / kr / zł multi-char currency prefixes
  • cli_format.py with auto-stream above 100 MB inputs

Encoding detection arbiter + language-aware probe:
  Closes the last 4 xfails (cp1250 / mac_iceland / shift_jis_2004 / lying-BOM)
  via tied-confidence arbiter + Cyrillic / EE-Latin coverage probes.

Distribution-readiness assets:
  • streamlit_app.py — Streamlit Community Cloud entry shim
  • src/gui/app_demo.py — single-page demo, ?p=<persona> routing,
    100-row cap + watermark, free-vs-paid boundary enforced at surface
  • samples/demo/ — 3 niche datasets + pre-tuned pipeline JSONs
  • landing/ — 4 static HTML pages (apex chooser + 3 niche),
    shared CSS, deploy.py URL-substitution script,
    auto-generated robots.txt + sitemap.xml + 404.html + favicon
  • docs/PLAN.md, DEMO-PLAN.md, DEPLOYMENT.md, POST-LAUNCH.md, NEXT-STEPS.md
    — full strategy + measurement + deployment + master checklist

Test counts:
  before: 1,520 passed · 4 skipped · 17 xfailed
  after:  1,729 passed · 0 skipped · 0  xfailed

Tier-1 corpora added:
  • missing-corpus           3 use cases + 16 edge cases
  • column-mapper-corpus     3 use cases + 5 edge cases
  • format-cleaner intl      20-row 13-country stress fixture

Engine hardening flushed out by the corpora:
  • interpolate guards against object-dtype columns
  • mean/median skip all-NaN columns (silences numpy warning)
  • fillna runs under future.no_silent_downcasting (silences pandas warning)
  • mojibake test no longer skips when ftfy installed (monkeypatch path)
  • drop-row threshold semantics: strict-greater (consistent across rows / cols)
  • currency_decimal validator allow-set updated for "auto"

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

tests/test_format_standardize_corpus.py

@@ -110,16 +110,16 @@ _DATE_EXPECTED_MDY: dict[str, object] = {
     "FD13": PASSTHROUGH,
     "FD14": PASSTHROUGH,
     "FD15": PASSTHROUGH,
-    # excel serial → 2024-01-15 (xfail — not implemented)
+    # excel serial dates (numeric days since 1899-12-30)
     "FD22": "2024-01-15",
     "FD23": "2024-01-15",
-    # unix timestamp seconds / millis → 2024-01-15 (xfail)
+    # unix timestamps (seconds, milliseconds)
     "FD24": "2024-01-15",
     "FD25": "2024-01-15",
     # partial precision — corpus preserves it
     "FD26": "2024-01",
-    "FD27": "2024-01",       # xfail — text precision
-    "FD28": "2024-Q1",       # xfail — quarter
+    "FD27": "2024-01",       # text precision month
+    "FD28": "2024-Q1",       # quarter
     "FD29": "2024",
     # 2-digit year cutoff (per docs: 1969 wins over 2069)
     "FD30": "1969-01-15",
@@ -135,7 +135,7 @@ _DATE_EXPECTED_MDY: dict[str, object] = {
     "FD37": "2024-01-15",
     # garbage → pass through (corpus 0.3 boundary table)
     # FD38/39/40 → PASSTHROUGH default
-    # locale-specific month names (xfail — not shipped)
+    # locale-specific month names (en/fr/de via month_locales)
     "FD41": "2024-01-15",
     "FD42": "2024-01-15",
     # timezone — corpus 3.3 says fixed-offset only