feat(mysql): CSV encoding and format options (#2601)

[Aias00]

Closes #2601

Summary

• New CsvParser shared by preview and execution: UTF-8/GB18030/ISO-8859-1 (strict decoding), single-char delimiter (comma/semicolon/tab/pipe), quote/escape chars, header toggle, CRLF/LF/CR detection, embedded newlines and quoted delimiters.
• Empty-field rule (empty string vs SQL NULL) applies identically to preview and import; invalid encoding / unclosed quote rejected with source line before any write.
• Formula-injection guard: values starting with = + - @ are single-quoted on import.
• Mapping modal: CSV options bar (encoding, delimiter, header, empty-field) that refreshes the bounded preview immediately.
• i18n ×5 + MYSQL-IMPORT-002 byte-accurate fixtures (GB18030/Latin-1, semicolon/tab, CRLF, no-header, bad-quote).

Test plan

• Run MYSQL-IMPORT-002 README verification (3 encodings, 4 delimiters, CRLF embedded newline, no-header, unclosed-quote rejection, empty-field rule, large-file bounded preview)

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[openai0229]

Follow-up review after the latest main integration: changes are still requested before merge.

This remains cumulative on #2652 and inherits its unchecked/full-file path handling, synchronous execution, DEFAULT placeholder mismatch, zero skipped count, and per-row batch/transaction problems. CSV options also need strict validation and source-line diagnostics for malformed encoding or quoting, with preview and execution sharing one bounded parsing/mapping contract. Please correct the cumulative implementation and rerun CI.

[openai0229]

Please sync this branch with the latest main and resolve the current conflicts before the next review. In particular, preserve the import preview and column-mapping behavior already merged through #2652 rather than replacing it with the older cumulative implementation. Once the branch is updated and CI has rerun on the new head, we can continue reviewing the CSV-specific changes.