feat(inspector): native CSV/TSV document inspector

[datlechin]

Summary

Closes #1259.

Adds a native macOS document-based CSV/TSV inspector. Open .csv and .tsv files directly from Finder, drag-and-drop, or File > Open. Each file opens as its own NSDocument-backed window (separate from connection windows, own tab group).

Capabilities

• Streaming/indexed data layer: memory-mapped file + one-pass quote-aware row index + on-demand single-column decode. Large files (tested with 350 MB / 2M rows) load without copying into memory.
• Edit cells, undo/redo (single keystroke cell edit = one undo step; bulk delete or paste = one undo step).
• Multi-condition filter (Cmd+F) with column / operator / value clauses (AND).
• Multi-column sort via shift-click on column headers, numeric fast path for typed numeric columns, precomputed natural-sort key for text columns ("Item 2" before "Item 10").
• Filter/sort run on the cooperative thread pool via Task.detached, cancellable on every new request, with an "Updating…" indicator in the status bar.
• Toolbar: Add Row, Delete, Columns menu (rename / insert before-after / type override / delete), Filter.
• Copy/paste selected rows as TSV via Cmd+C / Cmd+V.
• NSFilePresenter: auto-reload when no local edits, sheet prompt when there are unsaved edits. Mtime-based guard prevents self-write feedback loops.
• Per-document windowFrameAutosaveName so each file remembers its own window position.
• canConcurrentlyReadDocuments(ofType:) returns true so initial indexing runs off the main thread.

Tests

40 tests in TableProTests/Plugins/CSVInspectorTests.swift + TableProTests/Core/NaturalSortKeyTests.swift covering dialect detection (BOM, delimiter, line ending, encoding), streaming parser (quote handling, RFC 4180 escape, single-column field decode), row store (snapshot, bulk removeRows, column ops), writer round-trip (byte-perfect for unmodified rows, BOM preserved), and natural-sort key semantics (case-insensitive, leading zeros, embedded numbers).

Docs

• New docs/features/csv-inspector.mdx covering open / edit / column ops / filter / sort / copy-paste / external-change behavior.
• docs/features/keyboard-shortcuts.mdx updated with Cmd+F, Cmd+C, Cmd+V, and shift-click multi-sort.
• CHANGELOG.md entry under [Unreleased].

Test plan

• Open a small CSV from Finder, edit a cell, Cmd+S, reopen, edit persists.
• Open a 100K+ row CSV, sort by a text column, filter by a value, paginate, verify natural ordering.
• Open the 350 MB / 2M-row test file from feat: CSV inspection #1259, confirm main thread stays responsive during indexing (window appears after a brief delay, other windows usable).
• Select rows, Delete (or toolbar -), confirm next row is selected and arrow keys keep navigating.
• Toolbar Add Row from page 1 of a paginated file: jumps to new row's page with it selected.
• Columns menu: rename, insert before/after, delete, change type — each one undoable.
• Cmd+C copies selected rows as TSV (paste into a text editor to verify), Cmd+V from TSV appends new rows.
• Modify the file in another app while open with no local edits — auto-reloads. With unsaved edits — prompts.