feat: git SHA version badge in admin, fix finanzplan caching, drop gitea remote

- AdminShell: shows NEXT_PUBLIC_GIT_SHA in sidebar footer
- Dockerfile + build-pitch-deck.yml: pass --build-arg GIT_SHA at build time
- FinanzplanSlide: fetch with cache:no-store to always show current DB values
- finanzplan routes: Cache-Control: no-store to prevent CDN/proxy staling
- CLAUDE.md: remove dead gitea remote (only origin exists)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pitch-deck/app/api/finanzplan/[sheetName]/route.ts

@@ -39,7 +39,9 @@ export async function GET(
     query += ' ORDER BY sort_order'
 
     const { rows } = await pool.query(query, params)
-    return NextResponse.json({ sheet: sheetName, rows })
+    return NextResponse.json({ sheet: sheetName, rows }, {
+      headers: { 'Cache-Control': 'no-store' },
+    })
   } catch (error) {
     return NextResponse.json({ error: String(error) }, { status: 500 })
   }

pitch-deck/app/api/finanzplan/route.ts

@@ -25,6 +25,8 @@ export async function GET() {
       sheets,
       scenarios: scenarios.rows,
       months: { start: '2026-01', end: '2030-12', count: 60, founding: '2026-08' },
+    }, {
+      headers: { 'Cache-Control': 'no-store' },
     })
   } catch (error) {
     return NextResponse.json({ error: String(error) }, { status: 500 })