feat(datagrid): mask sensitive columns in the results grid

[iamthenuggetman]

Closes #485

What

Columns whose name matches a sensitive pattern (password, email, token, ssn, …) now render as a •••••• placeholder in the results grid instead of the real value.

• Per-cell reveal: masked cells show an eye button that reveals just that cell; a revealed cell gets an eye-off button to re-mask it
• Per-column reveal: masked column headers show an eye toggle that reveals / re-masks the whole column
• Edit guard: masked cells can't be edited (double-click, Enter, F2) until revealed, and the hover tooltip is suppressed so it can't leak the value
• Reveal state is grid-local and resets when the result data changes

Masking is display-only: copy (⌘/Ctrl+C, context menu) and export keep the real values, as requested in the issue. Write-path anonymization for exports is tracked separately in #483.

Settings

New Settings → Privacy tab:

• On/off toggle for masking (default: on)
• Editable column-name patterns (one per line, case-insensitive substring match)
• Per-connection include/exclude overrides as table.column entries — exclude wins over include, which wins over name patterns

Implementation

• src/utils/columnMasking.ts — pattern/overrides matching logic
• DataGrid.tsx / DataGridRow.tsx — masked rendering + reveal toggles
• SettingsContext.ts — columnMaskingEnabled / columnMaskingPatterns / columnMaskingOverrides settings
• PrivacyTab.tsx + tab registration in Settings.tsx
• i18n strings for all 11 locales

Tests

• 8 unit tests for the matching logic (tests/utils/columnMasking.test.ts)
• 5 DataGrid tests: placeholder rendering, column reveal/re-mask, per-cell reveal/re-mask, copy keeps the real value, edit guard on masked cells
• Full suite green (3443 tests), tsc -b and eslint clean