apply_changes UI: assign + milestone in the dialog and Reginald's tool (#24)

Surfaces the assign/milestone mutations end-to-end so they're usable in-app and
by the agent — the rest of #24.

Agent path:
- propose_change tool + system prompt now accept `assignee` (login/null) and
  `milestone` (id/null). ProposeChangeArgs + proposalsFor extended: a new
  ProposalContext (current assignee/milestone + milestones list) lets a proposal
  skip no-ops and label the milestone. ChangeProposal gains an always-present
  `summary` (plan is now label-only) — chat-panel, use-chat, and the model
  executor render `summary`, so non-label proposals display correctly.

Dialog path:
- Client `listCollaborators()` (prepends the repo owner — /collaborators omits
  them, so a solo-owner repo still has an assignable person). New
  `gitea:collaborators` bridge. The Adjust dialog gains Assignee + Milestone
  pickers (current values from the reconciled backlog); pending assign/remilestone
  changes flow through the existing apply path.

Tests: +4 core (assign/milestone proposals with no-op skip; collaborators
owner-prepend + no-double-add). 138 core green; core + desktop typecheck clean;
14 fixture e2e green; live-backlog now drives the pickers on real data.
Fixed stale P2 refs in live-backlog (P2 is shipped → correctly off the runway).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/desktop/src/main/gitea.ts

@@ -333,6 +333,17 @@ export function registerGiteaIpc(): void {
     }
   })
 
+  // Assignable people (repo collaborators) for the Adjust dialog's assignee picker.
+  ipcMain.handle('gitea:collaborators', async () => {
+    const client = getGiteaClient()
+    if (!client) return []
+    try {
+      return await client.listCollaborators()
+    } catch {
+      return []
+    }
+  })
+
   // ---- config (team onboarding) ----
   ipcMain.handle('config:get', () => publicConfig())
 

apps/desktop/src/main/model.ts

@@ -13,7 +13,6 @@ import {
   type ChangeProposal,
   type ChatMessage,
   createChatClient,
-  describeChange,
   type ModelRouter,
   type ProjectView,
   proposalsFor,
@@ -130,10 +129,19 @@ export function registerModelIpc(): void {
         const a = (args ?? {}) as ProposeChangeArgs
         const issue = await client.getIssue(a.issue).catch(() => null)
         if (!issue) return { error: `issue #${a.issue} not found` }
-        const built = proposalsFor(a, issue.labels, issue.title)
+        // Milestone titles + current assignee/milestone let a proposal label the
+        // milestone and skip a no-op assign/move.
+        const milestones = (a.milestone !== undefined ? await client.listMilestones().catch(() => []) : []).map(
+          (m) => ({ id: m.id, title: m.title }),
+        )
+        const built = proposalsFor(a, issue.labels, issue.title, {
+          currentAssignee: issue.assignee,
+          currentMilestoneId: issue.milestone?.id ?? null,
+          milestones,
+        })
         proposals.push(...built)
         return built.length
-          ? { proposed: built.map((p) => ({ issue: a.issue, diff: describeChange(p.plan) })) }
+          ? { proposed: built.map((p) => ({ issue: a.issue, diff: p.summary })) }
           : { proposed: [], note: 'no change — already at that value' }
       }
       if (name === 'record_directive') {