Help screen, explore→set-connector-type Enter, settype UI polish.

- New `screen_help.cpp` (`screen_idx = 6`). Left column: menu of 13
  topics (Overview, Dashboard, Console, Palette, Explore,
  Connect/plug, set-connector-type, Signal types, NC pins, Analyze,
  Scripting, Save/restore, Quitting). Centre column: paragraphs of
  the focused topic, word-wrapped via `paragraph()` and scrollable.
  Right column: standard help panel.
- `help` bare → opens the screen; `help <name>` keeps the existing
  textual command-help behaviour for scripts.
- Dashboard `[h]` shortcut opens the screen, and the dashboard help
  panel (both the loaded and the no-system branch) lists it.
- Console: title gets the standard breadcrumb (`essim → console —
  type commands, read textual output`). Module/connection counters
  moved off (they live on the dashboard now).
- Explore Enter on a part jumps to `set-connector-type` with the
  exact-match index pre-computed in the filtered list (avoids the
  substring-match collision where `J20` would land on the wrong
  row when J200/J21 also matched).
- set-connector-type screen: bind `focused_entry` to `selected` on
  both menus so the cursor `>` tracks the selected row when state
  is pre-seeded from outside. Right column drops its strict
  `size(WIDTH, EQUAL, 40)` in favour of `flex`, and the `new type`
  input uses `xflex` so it actually stretches across the column.
- Esc on `set-connector-type` honours `screen_back_idx` — when
  entered via Enter on a part in `explore`, Esc returns to explore;
  otherwise it returns to the dashboard like every other screen.
  Standalone command entries explicitly reset the back-link.
- Net-member rows in the explore detail pane carry a
  `module\tsignal` payload so Enter opens the popup scoped to the
  peer module rather than mis-firing on the locally selected one.
  Same scheme for local-pin rows.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/tui/tui.hpp

@@ -55,6 +55,11 @@ class Tui {
 
     // ---- Screen orchestration ----
     int screen_idx;
+    // Where Esc should send the user *next* if they came via an inter-screen
+    // jump (e.g. Enter on a part in `explore` → set-connector-type). −1 means
+    // "no back-link, Esc goes to the dashboard like usual". Always reset
+    // after consumption to avoid stale links across unrelated navigation.
+    int screen_back_idx = -1;
 
     // ---- Connect screen state ----
     std::vector<std::string> connect_modules;
@@ -97,6 +102,10 @@ class Tui {
     // ---- Dashboard scroll state (0 = top; grows as the user scrolls down) ----
     int dashboard_scroll_offset = 0;
 
+    // ---- Help screen state ----
+    int help_topic_idx = 0;
+    std::vector<std::string> help_topic_names;  ///< populated by BuildHelpScreen
+
     // ---- Analyze screen state (unified verify + analyze) ----
     int analyze_focus_idx = 0;       ///< 0=issues 1=groups 2=types
     std::vector<std::string> analyze_issues;
@@ -186,6 +195,7 @@ private:
     ftxui::Component BuildExploreScreen();
     ftxui::Component BuildDashboardScreen();
     ftxui::Component BuildAnalyzeScreen();
+    ftxui::Component BuildHelpScreen();
     ftxui::Component BuildSignalTypeModal();
     ftxui::Component BuildPaletteModal();
     // Open palette (resets query/index, builds initial list).