Round 20: Tail sweep — search expansion, redirects, 404 jumps, revenue clarity

Global search now covers purchase orders, estimates, and batches. Added /privacy, /terms, /security, /cookies, /gdpr redirects to /legal/*, plus /docs → /api/v1/docs and /pricing → apex anchor. Revenue/Orders dashboard cards carry honest tooltips (gross, inc tax, not net of card fees). The 404 page no longer dead-ends — it offers 4 primary jumps and 10 section chips.