refactor: DRY cleanup — extract shared helpers, remove duplication across tools, LSP, overlays, and runtime

Eliminate ~500 lines of duplicate code across 31 files by extracting
shared functions, helpers, and consolidating repeated patterns.

Highlights:
- Toast helpers (toast_info/success/warning/error) on AppStateRest
- push_event() helper for turn-event queue (19 callers consolidated)
- log_write_edit_tool() shared fn (turn.rs + engine.rs ~50 lines saved)
- resolve_api_key() shared fn (spawn.rs + provider.rs)
- LSP call_positional() helper on LspClient
- lsp_cursor_params() shared schema for 4 tool files
-overlay_block() helper for consistent overlay title/border styling
- cycle_selected_index(), path_not_found/a_directory() helpers
- mark_dirty(), save_settings() on AppStateRest
- Remove redundant Err(e) => Err(e) arms in LSP tools
- Consolidate generate_workspace_tree (turn.rs → workspace.rs)
- Simplify background-review wrapper args in auto/mod.rs

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -19,11 +19,29 @@ pub mod todo;
 pub mod usage;
 
 use ratatui::layout::Rect;
-use ratatui::style::Style;
+use ratatui::style::{Modifier, Style};
+use ratatui::text::Span;
 use ratatui::widgets::{Block, Borders, Clear};
 use ratatui::Frame;
 use super::theme::Theme;
 
+/// Decorate an overlay block with a styled title and matching border color.
+///
+/// Every overlay renders a `Block` with a title bar in its variant colour
+/// and a matching border — this helper centralises the `Span::styled` +
+/// `border_style` boilerplate that was duplicated identically in 14 overlay
+/// modules.
+pub fn overlay_block(block: Block<'static>, title: &str, color: ratatui::style::Color) -> Block<'static> {
+    block
+        .title(Span::styled(
+            format!(" {title} "),
+            Style::default()
+                .fg(color)
+                .add_modifier(Modifier::BOLD),
+        ))
+        .border_style(Style::default().fg(color))
+}
+
 /// Compute a centered rectangle within `area` at the given percentage width
 /// and height. The result is always at least 40 cols wide and 10 rows tall.
 pub fn centered_rect(area: Rect, percent_x: u16, percent_y: u16) -> Rect {