v0.21.2 — Fixes and improvements

Smaller fixes that went out with this release.

• The sign-up page no longer has dead links. “Change plan” pointed at a section of the public site that had moved away, so the link did nothing; it now opens a plan comparison inside the app, with a way back to sign-up carrying the plan you picked. Switching the interface language on that page used to end on a missing page — the language now switches on the spot.
• Corrections no longer inflate the dashboard total. The gross total on the invoices widget added up a correction and the invoice it corrects as two unrelated documents, so the same sale was counted twice — an invoice of 1,230 zł later corrected to 984 zł added 2,214 zł to the total instead of 984 zł. The breakdown now applies the correction to the document it corrects, exactly like the other totals on the page already did. Nothing on your invoices changed: this was only ever a display fault on the dashboard, and everything sent to KSeF was always correct.