v2.18: Fixes from a full test run

Ten fixes found by using Sprintwise start to finish, the way a new Product Owner would.

• Long project names no longer push the page sideways on a phone.
• Epics in a Jira export or search are left unticked, as finished work is, and new epics aren't added by Sync.
• The report only compares the readiness of changed and unchanged stories once there are at least 3 of each.
• Net change says how much came from re-estimates, so a sprint that grew only that way adds up.
• "Import stories" (not "Import CSV") on the backlog, and an empty project mentions Jira.
• The key field explains STORY-1 and when to use the Jira key.
• Exported CSVs keep each story's type and epic, so re-importing keeps bugs as bugs.
• The demo sprint is always the last fortnight, so it never looks out of date.
• On a phone, statuses fit their box and the burn-up's labels are readable.
• The first project's name box has a visible label.