feat(convert-receipt): allow non-cash methods without account number

[ndomako10]

Problem

ConvertFrom-ReceiptFileName currently enforces that all non-Cash methods must include an account number:

if ($method -ne 'Cash' -and $account -eq '') {
    return (& $fail "Could not parse filename")
}

This prevents valid filenames such as:

yyMMdd Vendor $Amount Card

from being parsed successfully, even though the ADR defines Method and Account as optional.

As a result:

• Users must use placeholders like "----" for unknown accounts
• Parsing logic is enforcing a business rule that should instead be handled by flagging
• This creates inconsistency with how Cash is handled

Proposed Solution

Remove the requirement that non-Cash methods must include an account number in ConvertFrom-ReceiptFileName.

Allow parsing of filenames where:

• A valid method is present
• The account is omitted

Update Get-ReceiptFlag to treat:

• Non-Cash methods with empty account ("") as "Account unknown"
• Cash with empty account as valid (no flag)

This preserves separation of concerns:

• Parsing validates structure and token correctness
• Flagging handles completeness and data quality

Acceptance Criteria

• Filenames like yyMMdd Vendor $Amount Card parse successfully (OK = $true)
• Returned object includes:
  • Method = "Card"
  • Account = ""
• Get-ReceiptFlag returns "Account unknown" for non-Cash methods with empty account
• Cash with no account does not produce a flag
• Existing behavior for:
  • "xxxx" → "Account obfuscated"
  • "----" → "Account unknown"
    remains unchanged
• No regression in parsing or validation for existing valid filenames