feat(tui): add usage overlay and sidebar for displaying usage statistics and tasks

feat(tui): implement status bar with connection and turn state indicators
feat(tui): create workflow panel for agent status and progress visualization
feat(web): introduce web frontend interface with static file serving
feat(ws): add WebSocket interface for real-time communication and session management

apps/interfaces/tui/src/view/overlays/usage.rs

@@ -0,0 +1,98 @@
+//! Overlay: usage statistics — detailed token usage, API call count, edit/
+//! review/lesson activity counters, and session elapsed time.
+use crate::view::sidebar::compute_usage_summary;
+use crate::view::theme::Theme;
+use ratatui::style::{Modifier, Style};
+use ratatui::text::{Line, Span};
+use ratatui::widgets::{Block, Paragraph};
+use ratatui::Frame;
+
+/// Render the Usage overlay.
+pub fn render(
+    frame: &mut Frame,
+    area: ratatui::layout::Rect,
+    block: Block<'static>,
+    state: &crate::state::AppStateRest,
+) {
+    let block = block
+        .title(Span::styled(
+            " Usage ",
+            Style::default()
+                .fg(Theme::INFO)
+                .add_modifier(Modifier::BOLD),
+        ))
+        .border_style(Style::default().fg(Theme::INFO));
+    let runtime = state.session_runtime.as_ref();
+    let now_ms = chrono::Utc::now().timestamp_millis();
+    let summary = runtime.map(|r| compute_usage_summary(&r.usage, r.session_start, now_ms));
+    let (edit_count, lesson_count, review_count, consec_empty) =
+        runtime.map_or((0, 0, 0, 0), |r| {
+            (r.edit_count, r.lesson_count, r.review_count, r.consecutive_empty_reviews)
+        });
+    let mut lines = vec![
+        Line::from(Span::styled(
+            "  Token Usage",
+            Style::default()
+                .fg(Theme::INFO)
+                .add_modifier(Modifier::BOLD),
+        )),
+        Line::from(Span::raw("")),
+    ];
+    if let Some(s) = &summary {
+        lines.push(Line::from(Span::styled(
+            format!("  Main agent:     {} tokens", s.main_tokens),
+            Style::default().fg(Theme::TEXT),
+        )));
+        lines.push(Line::from(Span::styled(
+            format!("  Self-learning:  {} tokens", s.self_learning_tokens),
+            Style::default().fg(Theme::TEXT_MUTED),
+        )));
+        lines.push(Line::from(Span::styled(
+            format!("  Total:          {} tokens", s.total_tokens),
+            Style::default()
+                .fg(Theme::TEXT)
+                .add_modifier(Modifier::BOLD),
+        )));
+        lines.push(Line::from(Span::styled(
+            format!("  API calls:      {}", s.api_calls),
+            Style::default().fg(Theme::TEXT),
+        )));
+    } else {
+        lines.push(Line::from(Span::styled(
+            "  No active session.",
+            Style::default().fg(Theme::TEXT_DIM),
+        )));
+    }
+    lines.push(Line::from(Span::raw("")));
+    lines.push(Line::from(Span::styled(
+        "  Activity",
+        Style::default()
+            .fg(Theme::INFO)
+            .add_modifier(Modifier::BOLD),
+    )));
+    lines.push(Line::from(Span::styled(
+        format!("  Edits:          {edit_count}"),
+        Style::default().fg(Theme::TEXT),
+    )));
+    lines.push(Line::from(Span::styled(
+        format!("  Reviews:        {review_count}"),
+        Style::default().fg(Theme::TEXT),
+    )));
+    lines.push(Line::from(Span::styled(
+        format!("  Lessons:        {lesson_count}"),
+        Style::default().fg(Theme::TEXT_MUTED),
+    )));
+    lines.push(Line::from(Span::styled(
+        format!("  Empty reviews:  {consec_empty}"),
+        Style::default().fg(if consec_empty > 3 { Theme::WARNING } else { Theme::TEXT_DIM }),
+    )));
+    if let Some(s) = &summary {
+        lines.push(Line::from(Span::raw("")));
+        lines.push(Line::from(Span::styled(
+            format!("  Session: {}h {}m {}s", s.elapsed_hours, s.elapsed_minutes, s.elapsed_seconds),
+            Style::default().fg(Theme::TEXT_DIM),
+        )));
+    }
+    let paragraph = Paragraph::new(lines).block(block);
+    frame.render_widget(paragraph, area);
+}