Add file badges, menu icons, LSP diagnostics, robust compaction

- Files in chat: preview with type/size badges and file name; attachment chips
- Menu and settings tabs with icons
- Heatmap: distinct colour for empty hours, hourly labels
- Context chip shows used/total tokens (e.g. 221k/240k) plus percent
- LSP client: diagnostics appended to edit/write results and a diagnostics tool
  (typescript-language-server, pyright, rust-analyzer, gopls, clangd; sandboxed)
- Compaction summarizes a plain transcript and retries once on empty output
- files/stat endpoint

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/i18n/de.ts

@@ -410,6 +410,7 @@ export const de: Messages = {
   "stats.prefillSpeed": "Prefill-Geschwindigkeit",
   "stats.costPerDay": "Kosten pro Tag nach Modell",
   "stats.tokensPerDay": "Tokens pro Tag",
+  "stats.heatEmpty": "keine Aktivität",
   "stats.heatmap": "Aktivität nach Wochentag und Uhrzeit",
   "stats.byModel": "Nach Modell",
   "stats.byProvider": "Nach Provider",