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/en.ts

@@ -409,6 +409,7 @@ export const en = {
   "stats.prefillSpeed": "Prefill speed",
   "stats.costPerDay": "Cost per day by model",
   "stats.tokensPerDay": "Tokens per day",
+  "stats.heatEmpty": "no activity",
   "stats.heatmap": "Activity by weekday and hour",
   "stats.byModel": "By model",
   "stats.byProvider": "By provider",