M9: kvitt-import Splitwise importer (SPEC §10.8, FR-17)

CLI per §10.8 with --help, --dry-run and a summary; English and Swedish
headers with member columns matched by name; CSV quoting; payments as
settlements with one allocation; trailing totals row used to reconcile
the account balance (mismatch rolls back, exit 4); non-SEK rows abort
unless --fx; committed category table data/splitwise_categories.csv;
idempotent re-runs through import_key; rows validated with the server's
push checks, audited with source import, no pushes; one BEGIN IMMEDIATE
transaction. Tests over synthetic fixtures only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

server/crates/kvitt-import/tests/fixtures/swedish.csv

@@ -0,0 +1,10 @@
+Datum,Beskrivning,Kategori,Kostnad,Valuta,Robin Sample,Alex Example
+
+2025-02-01,Matkasse,Livsmedel,200.00,SEK,-100.00,100.00
+2025-02-02,"Lampa, golv",Möbler,80.00,SEK,40.00,-40.00
+2025-02-03,Okänd sak,Påhittad kategori,10.00,SEK,5.00,-5.00
+2025-02-04,Betalning till Alex,Betalning,55.00,SEK,55.00,-55.00
+2025-02-05,Biljett,Buss/tåg,30.00,SEK,-15.00,15.00
+
+2025-02-06,Totalsumma, , ,SEK,-15.00,15.00
+