v0.3.0

Date handling overhaul, docs site, and reliability fixes

• Added documentation site with full command reference, backend guide, and changelog
• Overhauled date handling — index-based detection now works correctly in --no-header mode across read, search, export, and probe. Midnight datetimes normalised to date-only strings
• Added INVALID_REGEX structured error for malformed regex patterns in search --regex (including Rust regex engine incompatibilities)
• Fixed print area optimisation in LibreOffice _prepare_sheet_for_export for better PDF export
• Added save-path guard in format and sheet commands — non-writable extensions now fall back to .xlsx instead of silently saving OOXML content with the original extension
• Updated skill and command reference docs for output format clarity (--format csv|markdown), --in-formulas output schema, and engine availability per command

Full changelog: v0.2.0...v0.3.0