feat: add documentation, Streamlit GUI, and full source tree

- Rewrite README.md with project overview, quick-start, and CLI summary
- Add docs/CLI-REFERENCE.md with full flag reference and 8 recipe sections
- Add docs/DEVELOPER.md with architecture, data flow, and extension guides
- Rewrite src/core/__init__.py with public API exports and module docstring
- Add Streamlit GUI (src/gui/) with file upload, advanced options, interactive
  match group review with side-by-side diff, and download buttons
- Add .gitignore, requirements.txt, all source code, tests, and sample data
- Add streamlit to requirements.txt

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

samples/messy_sales_removed.csv

@@ -0,0 +1,28 @@
+order_id,customer_name,email,phone,address,product,amount,date
+1002,John Smith,johnsmith@gmail.com,555-123-4567,123 Main St Apt 4,Widget Pro,49.99,2024-01-15
+1003,Mr. John Smith,john.smith+promo@gmail.com,+1 555-123-4567,123 Main St. Apartment 4,Widget Pro,,2024-01-15
+1005,Sara Johnson,sarah.j@example.com,555.234.5678,456 Oak Ave,Gadget X,89.99,2024-02-03
+1006,Sarah M. Johnson,sarahj@example.com,5552345678,456 Oak Ave Suite 2,,89.99,2024-02-05
+1008,Mike Williams,mike.w@company.org,555-345-6789,789 Pine Blvd,Super Tool,129.99,2024-02-10
+1009,Dr. Michael Williams III,michael.williams@company.org,+15553456789,789 Pine Blvd,,129.99,2024-02-12
+1011,Emily Davis,emily.davis@mail.com,(555) 456-7890,321 Elm Drive,Basic Set,29.99,2024-03-01
+1013,Bob Brown,r.brown@email.net,555-567-8901,654 Cedar Ln,Premium Kit,199.99,2024-03-15
+1014,Robert J. Brown Jr.,rj.brown@email.net,5555678901,654 Cedar Lane,Premium Kit,,2024-03-17
+1016,Jennifer Wilson,jen.wilson@web.io,(555) 678-9012,987 Birch Ct,Starter Pack,19.99,2024-04-01
+1018,David Martinez,d.martinez@service.com,555-789-0123,246 Maple Rd,Deluxe Widget,79.99,2024-04-15
+1020,Lisa M Anderson,lisa.a@domain.com,555-890-1234,135 Walnut Way,Mini Tool,14.99,2024-05-01
+1022,Tom Taylor,tom.taylor@inbox.com,555-901-2345,864 Spruce Trl,Combo Pack,59.99,2024-05-15
+1025,Karen White,karen.w+newsletter@test.com,555-012-3456,579 Ash Cir,Widget Pro,49.99,2024-06-01
+1027,James Clark,j.clark@biz.co,555-111-2222,111 1st St N,Enterprise License,499.99,2024-06-15
+1029,Pat Lee,pat.lee@mail.com,555-222-3333,222 2nd Ave S,Basic Set,29.99,2024-07-01
+1031,Chris Hall,chris.hall@email.org,555-333-4444,333 3rd Blvd E,Gadget X,89.99,2024-07-15
+1033,Amanda Young,amanda.y@web.net,(555) 444-5555,444 Oak Pkwy,Super Tool,129.99,2024-08-01
+1035,Dan King,dan.king@corp.io,555.555.6666,555 Elm Sq,Premium Kit,199.99,2024-08-15
+1037,Michelle Scott,m.scott@place.com,(555) 666-7777,666 Pine Hwy,Deluxe Widget,79.99,2024-09-01
+1039,Kevin Adams,kevin.a+deals@shop.biz,555-777-8888,777 Cedar Ter,Starter Pack,19.99,2024-09-15
+1041,Nancy Wright,nancy.w@home.net,(555) 888-9999,888 Maple Pl,Mini Tool,14.99,2024-10-01
+1043,George Lopez,g.lopez@firma.com,555-999-0000,999 Walnut Expy,Combo Pack,59.99,2024-10-15
+1045,Sandra Hill,s.hill@provider.co,555-101-2020,1010 Spruce Xing,Widget Pro,49.99,2024-11-01
+1047,Mark Robinson,mark.r@office.com,555-202-3030,2020 Ash Hts,Enterprise License,499.99,2024-11-15
+1049,Unique Customer Two,unique2@solo.com,(555) 000-0002,2 Unique Road,Gadget X,89.99,2024-12-02
+1050,Unique Customer Three,unique3@solo.com,(555) 000-0003,3 Unique Road,Super Tool,129.99,2024-12-03