feat: Square payment integration, booking flow redesign, and timezone/weekday fixes

- Add Square payment integration (mock + handlers + UI): terminal/online payments,
  refunds, tips, saved cards, webhooks. Build-tagged dev/prod clients.
- Redesign booking flow: Step 4 conditional (deposit only), Step 5 confirmation
  screen with booking ID, auto-submit on transition.
- Redesign schedule modal: 2x3 button grid with Pay Deposit/Pay Early logic.
- Add deposit warning banner at Step 1 for users with outstanding deposits.
- Fix weekday conversion bug: Go 0=Sunday vs DB 0=Monday mismatch in 6 locations.
- Fix timezone bug: UTC vs London time in closing hours validation.
- Fix frontend error parsing: plain text backend errors now displayed correctly.
- Fix crypto.randomUUID fallback for environments without Web Crypto.
- Add 7 new regression tests: closing hours, advance check, active booking limit,
  weekday conversion, UTC/London, deposit snapshot, exceptional hours.
- Fix 3 flaky tests: dynamic dates instead of fixed, no-show timing.

local-dev-2.sh

@@ -134,6 +134,10 @@ tmux set-environment -t $SESSION_NAME S3_SECRET_KEY "$S3_SECRET_KEY"
 tmux set-environment -t $SESSION_NAME S3_BUCKET "$S3_BUCKET"
 tmux set-environment -t $SESSION_NAME AWS_REGION "$AWS_REGION"
 tmux set-environment -t $SESSION_NAME VITE_BACKEND_URL "$VITE_BACKEND_URL"
+tmux set-environment -t $SESSION_NAME SQUARE_ACCESS_TOKEN "${SQUARE_ACCESS_TOKEN:-}"
+tmux set-environment -t $SESSION_NAME SQUARE_LOCATION_ID "${SQUARE_LOCATION_ID:-}"
+tmux set-environment -t $SESSION_NAME SQUARE_ENVIRONMENT "${SQUARE_ENVIRONMENT:-mock}"
+tmux set-environment -t $SESSION_NAME SQUARE_WEBHOOK_SIGNATURE_KEY "${SQUARE_WEBHOOK_SIGNATURE_KEY:-}"
 
 # Pane 0: Database
 tmux send-keys -t $SESSION_NAME 'docker exec -it postgres psql -U myuser -d mydb -c "SELECT relname AS table_name, n_live_tup AS row_count FROM pg_stat_user_tables ORDER BY table_name;"'
@@ -1045,7 +1049,7 @@ echo -e "${C_GREEN}⏳ Running tests...${C_RESET}"
 cd /home/popertots/Crussell/backend
 export POSTGRES_USER POSTGRES_PASSWORD POSTGRES_HOST POSTGRES_DB GO_TESTING=1
 TEST_OUTPUT_FILE=$(mktemp)
-go test -tags test -v -p 1 -count=1 ./... 2>&1 | tee "$TEST_OUTPUT_FILE" || true
+go test -tags "test,dev" -v -p 1 -count=1 ./... 2>&1 | tee "$TEST_OUTPUT_FILE" || true
 TEST_OUTPUT=$(cat "$TEST_OUTPUT_FILE")
 rm -f "$TEST_OUTPUT_FILE"
 cd ..