Add pull request milestone features

TESTING.md

@@ -192,6 +192,11 @@ xcrun simctl launch booted de.rfc1437.gotcha
 - [ ] The list defaults to the saved Open/Closed filter.
 - [ ] Change the native filter menu between Open and Closed; the checkmark,
       rows, and persisted selection update.
+- [ ] Select a milestone and then All Milestones; the checkmark and pull-request
+      rows update, and the milestone selection persists independently per
+      server after relaunch.
+- [ ] The pull-request filter icon uses a neutral color for Open + All
+      Milestones and the app accent color whenever either filter is non-default.
 - [ ] Each row shows repository/number, title, author/update metadata, comment
       count, and draft/merged state where applicable.
 - [ ] Open a pull request and verify title, metadata, Markdown body, comments,
@@ -204,8 +209,8 @@ xcrun simctl launch booted de.rfc1437.gotcha
       both open and closed milestones.
 - [ ] Each milestone shows its title, description, state, due date, issue
       counts, and a green/amber closed/open progress bar.
-- [ ] Open a milestone and verify every assigned issue is listed; tapping an
-      issue opens its normal issue detail.
+- [ ] Open a milestone and verify every assigned issue and pull request is
+      listed; tapping either opens its normal detail.
 - [ ] Repository issue lists and issue details show the assigned milestone with
       a flag icon instead of a text label.
 - [ ] Repositories without milestones show the native empty state.