feat(format): per-cell standardizers + 199-row buyer corpus

Adds src/core/format_standardize.py — a per-cell standardizer for dates,
phones, emails, addresses, names, currencies, booleans — wired through
StandardizeOptions / standardize_dataframe with FieldType registry.

Includes:
- Date parser handles ISO/US/EU/longform/excel-serial/unix-timestamp/
  partial-precision/quarter notation; opt-in French/German/Spanish month
  dictionaries via month_locales.
- Phone via libphonenumber with extension preservation (;ext=N), 001
  international prefix handling, error sentinels for placeholders /
  multi-number cells.
- Email lowercase/trim/mailto/angle-bracket strip with optional
  --gmail-canonical mode.
- Address USPS abbreviation expansion or compression (expand=False per
  corpus § 6.3), state-name → 2-letter conversion, multi-line collapse,
  PO Box normalization, state-code preservation regardless of input case.
- Name handler: Mc/Mac/O'/D' inner caps, hyphen segments, particle
  lowercasing (von/van/de/da), comma-format reversal, period stripping
  for titles/suffixes/initials, PhD/MD acronym preservation, conservative
  mode for mixed-case input.
- Currency: auto-detect EU vs US separators, space-thousands, Swiss
  apostrophe, accounting parens, optional ISO code preservation, error
  sentinels for percentages/ranges/word-values/ambiguous separators.
- Per-domain error_policy ("passthrough" | "sentinel") for surfacing
  malformed values as <error: reason> per corpus § 0.3.

Test corpus from Business/DataTools/test-cases-format-cleaner copied to
test-cases/format-cleaner-corpus/ — 7 fixtures plus FORMATS-CASES.md.
tests/test_format_standardize_corpus.py drives all 199 rows through the
per-cell standardizers; 0 xfailed.

Wires the GUI page (3_Format_Standardizer.py) to "Ready" status.

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

src/gui/tools_registry.py

@@ -68,7 +68,7 @@ TOOLS: list[Tool] = [
             "Standardize dates, currencies, names, phone numbers, and addresses."
         ),
         page_slug="3_Format_Standardizer",
-        status="Coming Soon",
+        status="Ready",
     ),
     Tool(
         tool_id="04_missing_handler",