UX review flow and consistency fixes #19

Flow and consistency fixes from the UX review.

• After creating an issue, IssueListView.swift:92-98 closes the sheet and reloads the list. Open the new issue (IssueRoute.issue(repo:number:)) so triage is on screen.
• MR sections run Milestone, Labels, Stack, Superseded, Reviewers, Commits, Checks, Gates, … (MRView.swift:45-62). Put Gates and Checks directly under the description.
• Notifications open from a Dashboard toolbar button, with push settings above the inbox (NotificationsView.swift:20). Badge the Dashboard tab with the unread count and move push settings to the bottom.
• The build filter sheet expands from half to full height on the first tap, so that tap misses the Status picker. Present it at .large.
• #N and owner/name#N stay plain text in threads; the web links them. Resolve both in FormattedBodyView.
• Issue state is lowercase (IssueView.swift:75), MR state is capitalised, and the MR filter says "Gone" where chips say "source gone". Pick one casing; "Merge requests" in sentence case.
• Repository settings copy says "mr merge becomes their only writer"; use "merging a merge request becomes the only way to change them".
• SSH key removal and repository rename are one-tap dialogs; the web asks for the typed name. Use a typed-name field for those two.
• No iPad layout: no NavigationSplitView anywhere. Use one for Repositories and Dashboard at regular width.