refactor: massive codebase restructuring — naming, splitting, DRY

Crate renames:
  - zesdex-entities::seaorm → domain (misleading name, no SeaORM used)
  - zesdex-dto → merged into zesdex-entities (100% re-exports)
  - zesdex-libs → zesdex-infra (vague name)

Module renames:
  - app/harness → guard (misleading: safety gatekeeper, not test harness)
  - runtime/commands → action_dispatch (name clashed with controller/command)
  - resources → prompts (embedded prompt text, not general resources)
  - tool/seqthink → sequential_think (unreadable abbreviation)
  - msglog/query → insert (module only inserts, never queries)

Dead code removal:
  - app/mode/help.rs (orphaned — not declared in mod.rs)
  - app/mode/loading.rs (orphaned — not declared in mod.rs)

File splitting (71 new files, avg ~115 lines/file):
  - app/runtime/actions/: 1→8 files (was 2030 lines)
  - view/overlays/: 1→16 files (was 1167 lines)
  - tool/lsp/: 1→8 per-tool files (was 909 lines)
  - main.rs: 1→5 files (session, daemon, attach, event_loop)
  - workflow/engine + hive_mind: 2→10 files
  - subagent/engine + auto: 2→9 files
  - lsp/provisioner: 1→5 files
  - review/: 1→6 files
  - guard/: 1→2 files (extracted patterns)
  - state/misc: 1→3 files (input, scroll)
  - mcp/: 1→3 files (transport, adapter)
  - stream/json_repair extracted from turn.rs

DRY:
  - Pattern constants (STUB_PATTERNS etc) in guard/patterns shared with subagent
  - 3 near-identical background spawners → 1 generic + thin wrappers
  - Shared spawn_subagent_with_drain() extracted
  - Shared create_session() in main
  - write_osc52 deduplicated

Bug fixes:
  - archive_message(): sess.db → db (wrong variable name)
  - execute_one_tool(): wrong parameter name
  - check_credential_read() function was missing (restored from test expectations)

crates/zesdex-backend/src/view/overlays/usage.rs

@@ -0,0 +1,115 @@
+use ratatui::style::{Modifier, Style};
+use ratatui::text::{Line, Span};
+use ratatui::widgets::{Block, Paragraph};
+use ratatui::Frame;
+use crate::view::theme::Theme;
+
+pub fn render(
+    frame: &mut Frame,
+    area: ratatui::layout::Rect,
+    block: Block<'static>,
+    state: &crate::app::state::rest::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| {
+        crate::view::sidebar::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:  {}",
+            if consec_empty > 3 {
+                format!("{consec_empty} ⚠")
+            } else {
+                consec_empty.to_string()
+            },
+        ),
+        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);
+}