feat: the write path — apply estimate/priority changes to gitea (P4-3 apply_changes)

The first write path. Read, forecast, and calibration were all real; now you can
*manage* CommiTea from CommiTea. Estimates/priority are exclusive label axes, so
a change is a label swap — proposed, approved, then written. Nothing is assumed.

core (@commitea/core):
- planIssueChange(current, change): pure diff planner — swaps the est/*|p/* axis,
  clears on null, dedups a doubled axis; returns the resulting label set + a
  before/after diff + noop flag. describeChange() renders "est/2d → est/5d".
- request() seam extended for writes (method/body, JSON, 204). client gains
  listLabels() (name→id) and setIssueLabels() (PUT /issues/{n}/labels).

app:
- main bridge gitea:applyChange — resolves plan.labels → ids (cached, refetch on
  miss), PUTs, returns the plan + fresh issue. Token never leaves main.
- preload + global.d.ts expose applyChange; useBacklog returns a refetch so a
  write re-reconciles the board + forecast.
- Issue screen: an Adjust button (shown only when configured) opens a
  propose-approve Dialog — estimate/priority pickers, live "est/3d → est/8d"
  consequence, Apply/Cancel. AppShell wires it, reflects new labels on the open
  issue immediately, and refetches.

Verified: 83 core tests green (7 apply-changes + 2 client-write new), desktop
typecheck clean, 14 fixture e2e green. Live spec exercises propose + CANCEL (no
mutation); the real PUT was verified once manually (change #2 est/3d→est/8d→200,
reverted clean). Icon: pencil (no sliders-horizontal in the set).

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

apps/desktop/src/main/gitea.ts

@@ -9,7 +9,14 @@
 import { readFileSync } from 'node:fs'
 import { dirname, join } from 'node:path'
 
-import { createGiteaClient, type GiteaConfig, type LifecycleEvent } from '@commitea/core'
+import {
+  createGiteaClient,
+  type GiteaConfig,
+  type GiteaLabel,
+  type IssueChange,
+  type LifecycleEvent,
+  planIssueChange,
+} from '@commitea/core'
 import { ipcMain } from 'electron'
 
 /** Walk up from cwd looking for a .env.local with a GITEA_TOKEN (dev convenience). */
@@ -71,4 +78,31 @@ export function registerGiteaIpc(): void {
     if (!client) return null
     return client.getIssue(index)
   })
+
+  // Cached label list for name→id resolution; refreshed on demand if a name misses.
+  let labelCache: GiteaLabel[] | null = null
+  async function resolveLabelIds(names: string[]): Promise<number[]> {
+    if (!client) return []
+    const lookup = () => new Map(labelCache!.map((l) => [l.name, l.id]))
+    if (!labelCache) labelCache = await client.listLabels()
+    let byName = lookup()
+    if (names.some((n) => !byName.has(n))) {
+      labelCache = await client.listLabels() // a name we don't know — refetch once
+      byName = lookup()
+    }
+    return names.map((n) => byName.get(n)).filter((id): id is number => id != null)
+  }
+
+  // The write path (apply_changes). Additive label swaps, applied only after the
+  // renderer's propose-approve. Returns the plan + the freshly-read issue.
+  ipcMain.handle('gitea:applyChange', async (_event, change: IssueChange) => {
+    if (!client) return { ok: false as const, reason: 'unconfigured' as const }
+    const current = await client.getIssue(change.issue)
+    const plan = planIssueChange(current.labels, change)
+    if (plan.noop) return { ok: true as const, plan, issue: current }
+    const ids = await resolveLabelIds(plan.labels)
+    await client.setIssueLabels(change.issue, ids)
+    const issue = await client.getIssue(change.issue)
+    return { ok: true as const, plan, issue }
+  })
 }