Fix selected-file reparse behavior in import modal

Summary

After a user selects another import file, changing a CSV parse option can re-parse the original file instead of the selected file.

Required changes

Update the import modal parse flow to use the current selected filename for option-driven re-parses.

• In packages/desktop-client/src/components/modals/ImportTransactionsModal/ImportTransactionsModal.tsx, make the parsing effect use the current filename state rather than originalFileName.
• Include filename in the parsing effect dependency list.
• Change onNewFile to update the selected filename and let the effect perform the parse.
• Preserve the expected lastParseRef and preserveImportSettings behavior.
• Ensure selecting a new file does not cause duplicate parsing.

Rationale

The encoding selector follows the existing option-driven parsing pattern. The same selected-file issue also affects delimiter, header-row, and skip-line changes. This follow-up keeps the CSV encoding PR scoped to encoding support.

Affected area

• packages/desktop-client/src/components/modals/ImportTransactionsModal/ImportTransactionsModal.tsx

Acceptance criteria

• After selecting another file, changing csvEncoding, delimiter, header-row, or skip-line options parses the selected file.
• Selecting another file performs one parse.
• Existing import-settings preservation behavior remains correct.

References

• PR: https://github.com/actualbudget/actual/pull/8924
• Review comment: https://github.com/actualbudget/actual/pull/8924#discussion_r3996322191
• Requested by: @flafleur