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>

server/src/api.rs

@@ -92,6 +92,7 @@ pub fn router(app: AppState) -> Router {
         .route("/files/list", get(crate::files::list))
         .route("/files/read", get(crate::files::read))
         .route("/files/raw", get(crate::files::raw))
+        .route("/files/stat", get(crate::files::stat))
         .route("/files/write", put(crate::files::write))
         .route("/files/create", post(crate::files::create))
         .route("/files/move", post(crate::files::move_or_copy))