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/help.rs

@@ -1,5 +1,4 @@
-use ratatui::style::{Modifier, Style};
-use ratatui::text::Span;
+use ratatui::style::Style;
 use ratatui::widgets::{Block, Paragraph, Wrap};
 use ratatui::Frame;
 use crate::view::theme::Theme;
@@ -10,14 +9,7 @@ pub fn render(
     block: Block<'static>,
     _state: &crate::app::state::rest::AppStateRest,
 ) {
-    let block = block
-        .title(Span::styled(
-            " Help ",
-            Style::default()
-                .fg(Theme::INFO)
-                .add_modifier(Modifier::BOLD),
-        ))
-        .border_style(Style::default().fg(Theme::INFO));
+    let block = super::overlay_block(block, "Help", Theme::INFO);
     let content = crate::prompts::HELP_TEXT;
     let paragraph = Paragraph::new(content)
         .block(block)