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/e2e/live-backlog.spec.ts

@@ -11,6 +11,7 @@ const MAIN = join(here, '..', 'out', 'main', 'index.js')
 test.describe('live backlog', () => {
   test('The pot + Focus render real gitea data', async () => {
     test.skip(!process.env.GITEA_LIVE, 'GITEA_LIVE not set — opt-in live test')
+    test.setTimeout(90_000)
     const app = await electron.launch({ args: [MAIN], env: { ...process.env } })
     const win = await app.firstWindow()
     await win.waitForLoadState('domcontentloaded')
@@ -42,16 +43,17 @@ test.describe('live backlog', () => {
       win.getByText(/cold-start priors · \d+\/20 closed issues estimated|calibrated on \d+ closed/),
     ).toBeVisible()
     // Real per-milestone forecasts — these milestone names come from gitea, not the
-    // fixture (which lists Beta / Pilot-ready / v1.0).
-    await expect(win.getByText(/P2 — Scheduler/)).toBeVisible()
+    // fixture (Beta / Pilot-ready / v1.0). The runway shows milestones with open
+    // scope; P5 is active (P2 is fully shipped, so it's correctly omitted).
+    await expect(win.getByText(/P5 — Dogfood/)).toBeVisible()
     // Real capacity config from pm-state (christian/stephen), not the fixture (Stephen/Ana K.)
     await expect(win.getByText('christian', { exact: true })).toBeVisible()
     await expect(win.getByText(/pd\/day/).first()).toBeVisible()
     await win.screenshot({ path: join(here, '.artifacts', 'screens', 'live-runway.png'), fullPage: true, animations: 'disabled' })
 
-    // Milestone drill-in — clicking a real milestone opens its real detail
-    await win.getByText(/P2 — Scheduler/).click()
-    await expect(win.getByRole('heading', { name: 'P2 — Scheduler + Monte Carlo' })).toBeVisible()
+    // Milestone drill-in — clicking a real (active) milestone opens its real detail
+    await win.getByText(/P5 — Dogfood/).click()
+    await expect(win.getByRole('heading', { name: 'P5 — Dogfood + polish' })).toBeVisible()
     await expect(win.getByText(/\d+ issues · est \d+d/)).toBeVisible()
     await win.screenshot({ path: join(here, '.artifacts', 'screens', 'live-milestone.png'), fullPage: true, animations: 'disabled' })
     await rail.getByRole('button', { name: 'Runway' }).click()
@@ -68,10 +70,15 @@ test.describe('live backlog', () => {
     await win.getByRole('main').getByRole('link').first().click()
     await expect(win.getByText(/· stephen\/commitea/)).toBeVisible()
     await win.getByRole('button', { name: 'Adjust' }).click()
-    await expect(win.getByText('Adjust estimate & priority')).toBeVisible()
+    await expect(win.getByText('Adjust issue')).toBeVisible()
     await win.getByRole('combobox').first().selectOption('est/8d')
-    await expect(win.getByText('Proposed label change')).toBeVisible()
+    await expect(win.getByText('Proposed change')).toBeVisible()
     await expect(win.getByText(/est\/8d/).last()).toBeVisible()
+    // the unified tool also drives assignee + milestone — the pickers render and diff
+    await expect(win.getByText('Assignee', { exact: true })).toBeVisible()
+    await expect(win.getByText('Milestone', { exact: true })).toBeVisible()
+    await win.getByRole('combobox').nth(2).selectOption('') // Assignee → Unassigned
+    await expect(win.getByText('unassign', { exact: true })).toBeVisible()
     await win.screenshot({ path: join(here, '.artifacts', 'screens', 'live-apply-change.png'), fullPage: true, animations: 'disabled' })
     await win.getByRole('button', { name: 'Cancel' }).click() // no mutation