feat(git): add upstream tracking and local-only branch UI

This release adds upstream tracking for branches and a local-only
indicator in the UI.
The Git integration now exposes upstreams and supports publish flows.
This enables publishing and remote-tracking configuration.

- Introduces upstream tracking and local-only branch UI markers
- Updates toolbar to reflect publish-local state and status indicators
- Bumps version to 2026.8.3 and updates changelog

src/lib/RepoToolbar.svelte

@@ -3,6 +3,7 @@
     ChevronDown,
     Code2,
     CloudDownload,
+    CloudOff,
     Download,
     FolderOpen,
     GitCompare,
@@ -21,6 +22,7 @@
   export let operation: string = "";
   export let ahead: number = 0;
   export let behind: number = 0;
+  export let localOnly: boolean = false;
   export let language: "en" | "de" = "en";
   export let editorName: string = "Editor";
   export let terminalName: string = "Terminal";
@@ -45,6 +47,12 @@
   let toolbarElement: HTMLDivElement;
 
   $: isGerman = language === "de";
+  $: pushLabel = localOnly ? (isGerman ? "Veröffentlichen" : "Publish") : "Push";
+  $: pushTitle = localOnly
+    ? (isGerman
+      ? "Dieser Branch existiert nur lokal. Veröffentlichen erstellt den Remote-Branch und richtet das Tracking ein."
+      : "This branch exists only locally. Publish creates the remote branch and configures tracking.")
+    : "Push";
 
   function runHistoryAction(action: () => void) {
     historyOpen = false;
@@ -103,10 +111,13 @@
 
       <button
         class="repo-action sync-primary"
+        class:publish-local={localOnly}
         onclick={onPush}
         disabled={!hasRepository || isBusy}
-        title="Push"
-        aria-label={ahead > 0
+        title={pushTitle}
+        aria-label={localOnly
+          ? pushTitle
+          : ahead > 0
           ? `Push, ${ahead} ${isGerman ? (ahead === 1 ? "lokaler Commit voraus" : "lokale Commits voraus") : (ahead === 1 ? "commit ahead" : "commits ahead")}`
           : "Push"}
       >
@@ -115,8 +126,12 @@
         {:else}
           <Upload size={15} aria-hidden="true" />
         {/if}
-        <span class="repo-action-label">Push</span>
-        {#if ahead > 0}<span class="repo-action-count ahead">↑{ahead}</span>{/if}
+        <span class="repo-action-label">{pushLabel}</span>
+        {#if localOnly}
+          <span class="repo-action-local-marker"><CloudOff size={9} aria-hidden="true" />{isGerman ? "NUR LOKAL" : "LOCAL"}</span>
+        {:else if ahead > 0}
+          <span class="repo-action-count ahead">↑{ahead}</span>
+        {/if}
       </button>
       <div class="repo-history-wrap">
         <button class="repo-action" type="button" onclick={() => { syncOpen = !syncOpen; historyOpen = false; }} disabled={!hasRepository || isBusy} aria-label={isGerman ? "Sync-Optionen" : "Sync options"} aria-haspopup="menu">