refactor: rewrite export system with streaming and native macOS patterns

[datlechin]

Summary

• Rewrites the entire export/import pipeline from O(N^2) OFFSET/LIMIT pagination to O(N) AsyncThrowingStream-based streaming
• Native streaming implemented for all 14 database drivers (MySQL, PostgreSQL, SQLite, ClickHouse, MSSQL, Redis, MongoDB, Oracle, DuckDB, Cassandra, Etcd, CloudflareD1, DynamoDB, BigQuery)
• Fixes data correctness issues: JSON leading-zero corruption, XLSX silent truncation, CSV formula injection over-correction, MQL invalid JSON passthrough
• Replaces custom progress with NSProgress, blocking NSSavePanel with async sheet, non-atomic writes with crash-safe atomic writes

Changes (73 files, +3030/-962)

Performance

• All drivers stream rows one at a time instead of OFFSET/LIMIT batching
• MySQL: mysql_use_result + mysql_fetch_row
• PostgreSQL: PQsetSingleRowMode + PQgetResult
• SQLite: sqlite3_step loop
• ClickHouse: URLSession.bytes + JSONEachRow
• MSSQL: dbnextrow loop
• Redis: SCAN cursor streaming
• MongoDB: mongoc_cursor_next loop
• Oracle: OracleNIO AsyncSequence
• DuckDB: duckdb_fetch_chunk iteration
• Cassandra: automatic paging with cass_result_has_more_pages
• DynamoDB: ExclusiveStartKey pagination
• BigQuery: pageToken pagination
• Etcd/D1: single-request streaming

Data Correctness

• JSON: column-type-guided numeric inference, leading-zero strings preserved, BIGINT > Int.max emitted as raw integers
• XLSX: auto-splits at 1,048,576 rows with warning, ZIP64 overflow guard, atomic writes
• CSV: OWASP-only formula injection prefixes (= + - @)
• MQL: JSONSerialization validation before raw object passthrough

Native macOS

• NSProgress replaces custom PluginExportProgress/PluginImportProgress
• presentAsSheet(for:) replaces blocking NSSavePanel.runModal()
• Atomic file writes via temp file + FileManager.replaceItemAt
• Async gzip compression via Process.terminationHandler

Cleanup

• Deleted: ProgressUpdateCoalescer, ExportServiceState, ImportServiceState, ExportProgressProxy, SQLExportHelpers
• Removed redundant NSLock on @mainactor class
• PluginKit ABI version bumped (3 -> 4)

Closes #771

Test plan

• Export large MySQL table (>100K rows) as CSV, verify constant-time batches
• Export >1M rows as XLSX, verify auto sheet split + warning message
• Export JSON with leading-zero values (ZIP codes), verify preserved as strings
• Cancel export mid-stream, verify no partial file left at destination
• Export with gzip compression, verify async completion
• Multi-table export, verify progress reaches 100%
• Test each database driver's export individually