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/files.rs

@@ -259,6 +259,19 @@ pub async fn raw(Extension(user): Extension<User>, State(app): State<AppState>,
         .into_response())
 }
 
+#[derive(Deserialize)]
+pub struct StatQuery {
+    path: String,
+}
+
+/// Size, type and modification time of a file (captions in the chat).
+pub async fn stat(Extension(user): Extension<User>, State(app): State<AppState>, Query(q): Query<StatQuery>) -> ApiResult {
+    let p = checked_path(&app, &user, &q.path, true)?;
+    let m = tokio::fs::metadata(&p).await?;
+    let mtime = m.modified().ok().and_then(|t| t.duration_since(std::time::UNIX_EPOCH).ok()).map(|d| d.as_millis() as u64);
+    Ok(Json(json!({"size": m.len(), "dir": m.is_dir(), "mime": mime_for(&p), "mtime": mtime})))
+}
+
 #[derive(Deserialize)]
 pub struct WriteBody {
     path: String,