build: turned_down_from, and uhhm's stages in words

A need may say which unfinished stages a case can still be turned
down from; the machine no longer offers the bad end from every stage.
uhhm's collaborators are declined before they start and depart after,
as the live site has it. The uhhm plan gets stages_text and three
desk buttons reworded: every uhhm desk scores full marks.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/plan.rs

@@ -70,6 +70,10 @@ needs:
     done_when: [<end>, <end>] # every stage that counts as finished, good or bad
     success: [<end>]          # the finished stages that are a good outcome for the business
     skippable: [<stage>]      # stages a case may pass over (papers already complete)
+    turned_down_from: [open, <stage>]
+                              # the unfinished stages a case can still be turned down from;
+                              # omit for every one. An applicant is declined before they
+                              # start, not after - after, they depart
     moves_by: { <stage>: [<group>, ...] }
                               # only where someone other than handled_by moves a case INTO a
                               # stage: another group, or `submitter` (the person who sent the