refactor: Unify OperationType and Action enums

[przemyslawbialon]

Labels: refactor, good first issue, correctness
Priority: P1
Blocked by: #4 (plugin ABC refactor will touch these same files)

Context

Per TAX_LAW_AUDIT.md Issue #1: pit38/plugins/stock/revolut/transaction_row_parser.py:31 returns OperationType.BUY but Transaction expects Action.BUY. The code works only because both enums have the same .value = "BUY". This is fragile — any change to either enum breaks silently without a type error.

Good first issue for a Python developer because:

• Scope is narrow (two enums, handful of files)
• No tax-logic understanding needed
• Clear success criterion (mypy passes, tests pass)

Acceptance Criteria

• Either: merge OperationType and Action into a single enum used by both parsers and domain objects
• Or: add an explicit mapping function with a comment explaining why both exist
• mypy catches any future mismatch (once Consolidate operation and transaction reading from csv #9 is in, this should be automatic)
• All existing tests pass
• TAX_LAW_AUDIT.md updated: mark Issue Create a service for business logic of stock transactions  #1 as resolved

Technical Approach

Preferred: one enum. Look for all uses of OperationType and Action via grep -r "OperationType\|Action" pit38/. If the two enums have identical values, delete one and update all imports.

Alternative if semantics differ:

# pit38/domain/transactions/action.py
from enum import Enum

class Action(str, Enum):
    BUY = "BUY"
    SELL = "SELL"
    DIVIDEND = "DIVIDEND"
    # ... all values

# pit38/plugins/stock/revolut/transaction_row_parser.py
# Before: returns OperationType.BUY (wrong type, works by accident)
# After:
def _operation_type(row) -> Action:
    return Action[row["Type"].upper()]  # explicit parse

Related

• TAX_LAW_AUDIT.md Issue Create a service for business logic of stock transactions  #1
• Should be tackled after Check which rates table from NBP we should use for exchange rates #4 merges (ABC refactor touches same files)