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/rewind.rs

@@ -0,0 +1,68 @@
+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(
+            " Rewind ",
+            Style::default()
+                .fg(Theme::ACCENT_ORANGE)
+                .add_modifier(Modifier::BOLD),
+        ))
+        .border_style(Style::default().fg(Theme::ACCENT_ORANGE));
+    let mut lines: Vec<Line> = vec![
+        Line::from(Span::styled(
+            "  Use ↑↓ to navigate, Enter to rewind to that point",
+            Style::default().fg(Theme::TEXT_DIM),
+        )),
+        Line::from(Span::raw("")),
+    ];
+    let messages = &state.transcript_cache.messages;
+    if messages.is_empty() {
+        lines.push(Line::from(Span::styled(
+            "  No messages in current session.",
+            Style::default().fg(Theme::TEXT_DIM),
+        )));
+    } else {
+        let start = if messages.len() > 8 {
+            messages.len() - 8
+        } else {
+            0
+        };
+        for msg in &messages[start..] {
+            let role_str = match msg.role {
+                crate::dto::chat::message::Role::User => "User",
+                crate::dto::chat::message::Role::Assistant => "Asst",
+                crate::dto::chat::message::Role::System => "Sys",
+                crate::dto::chat::message::Role::Tool => "Tool",
+            };
+            let preview: String = msg.content.chars().take(70).collect();
+            lines.push(Line::from(Span::styled(
+                format!("  [{role_str}] {preview}"),
+                Style::default().fg(
+                    if matches!(msg.role, crate::dto::chat::message::Role::User) {
+                        Theme::INFO
+                    } else {
+                        Theme::TEXT
+                    },
+                ),
+            )));
+        }
+        if messages.len() > 8 {
+            lines.push(Line::from(Span::styled(
+                format!("  ... and {} more messages", messages.len() - 8),
+                Style::default().fg(Theme::TEXT_DIM),
+            )));
+        }
+    }
+    let paragraph = Paragraph::new(lines).block(block);
+    frame.render_widget(paragraph, area);
+}