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>

packages/core/src/gitea/client.ts

@@ -13,6 +13,7 @@ import {
   type FetchLike,
   type GiteaConfig,
   type GiteaIssue,
+  type GiteaLabel,
   type GiteaMilestone,
   type GiteaMilestoneRef,
 } from './types.js'
@@ -98,6 +99,10 @@ export interface GiteaClient {
   getIssueDependencies(index: number): Promise<number[]>
   /** Normalized lifecycle events for one issue (all pages of its timeline). */
   getIssueTimeline(index: number): Promise<LifecycleEvent[]>
+  /** Every label defined on the repo (id + name), for name→id resolution. */
+  listLabels(): Promise<GiteaLabel[]>
+  /** Replace an issue's entire label set with the given label ids. Write. */
+  setIssueLabels(index: number, labelIds: number[]): Promise<void>
 }
 
 /** Map raw gitea issue JSON to the normalized domain shape. Pure. */
@@ -144,18 +149,24 @@ export function createGiteaClient(config: GiteaConfig, fetchImpl: FetchLike): Gi
   const apiBase = `${config.baseUrl.replace(/\/+$/, '')}/api/v1`
   const repoBase = `${apiBase}/repos/${config.owner}/${config.repo}`
 
-  async function request(path: string): Promise<unknown> {
+  async function request(path: string, init?: { method?: string; body?: unknown }): Promise<unknown> {
+    const method = init?.method ?? 'GET'
+    const hasBody = init?.body !== undefined
     const res = await fetchImpl(`${repoBase}${path}`, {
+      method,
       headers: {
         Authorization: `token ${config.token}`,
         Accept: 'application/json',
+        ...(hasBody ? { 'Content-Type': 'application/json' } : {}),
       },
+      body: hasBody ? JSON.stringify(init!.body) : undefined,
     })
     if (!res.ok) {
       const body = await res.text().catch(() => '')
-      throw new GiteaApiError(res.status, `GET ${path} failed (${res.status})`, body)
+      throw new GiteaApiError(res.status, `${method} ${path} failed (${res.status})`, body)
     }
-    return res.json()
+    // writes may reply 204 No Content
+    return res.status === 204 ? null : res.json()
   }
 
   /** Follow gitea's page-limit pagination until a short page is returned. */
@@ -200,5 +211,16 @@ export function createGiteaClient(config: GiteaConfig, fetchImpl: FetchLike): Gi
       )
       return normalizeTimeline(raw)
     },
+
+    async listLabels() {
+      const raw = await requestAll<{ id: number; name: string }>(
+        (page) => `/labels?page=${page}&limit=${PAGE_LIMIT}`,
+      )
+      return raw.map((l) => ({ id: l.id, name: l.name }))
+    },
+
+    async setIssueLabels(index, labelIds) {
+      await request(`/issues/${index}/labels`, { method: 'PUT', body: { labels: labelIds } })
+    },
   }
 }