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>

DESIGN.md

@@ -182,7 +182,16 @@ The Connection record stores `Module*`/`Part*` for both endpoints (added to `Con
 
 **Signal-type popup (shared)**: Enter on a signal entry in the `explore` screen opens a modal (`Tui::sigtype_dialog_open`) that lets the user pick `power | gnd | other` for the currently-selected signal. Built in `screen_sigtype_modal.cpp::BuildSignalTypeModal()`, attached to both screens via the `Modal(...)` decorator in `Run()`. Inside the modal, Enter applies + closes + records `set-signal-type <m> <s> <t>` in the script-save buffer (`recorded`); Esc closes without applying. Two safeguards: (a) re-selecting the type the pin already has is a no-op and records nothing; (b) the recorder collapses consecutive edits of the same `(module, signal)` — if the previous line in `recorded` already targets the same pair, it is replaced rather than appended. The outer `CatchEvent` in `Run()` cedes Tab/Esc to the modal whenever `sigtype_dialog_open` is true, so the underlying screen doesn't yank focus back. In `explore` the popup also fires from the detail pane when browsing `parts`: each `pin → signal` row carries its signal name in the parallel `explore_detail_sig` vector, and Enter on a non-`(NC)` row opens the popup for that signal.
 
-**Net tracing in `explore`**: when the user selects a signal entry in `explore` (type tab = `signals`), the detail pane shows two sections: the local pins of that signal (module/part/pin labels), then — if `find_net(sys, module, signal)` returns ≥ 2 members — a `Net members (across connections)` section listing every `(module, signal, type)` reachable through `Connection::pin_map`. The signal-detail header includes `K net members across N module(s)` (or `INCONSISTENT` if `net_type_consistent` returns false). Members are sorted naturally and pushed into `explore_detail_sig` so pressing Enter on a member opens the signal-type popup for it. This is what replaced the former dedicated `net` screen.
+**Net tracing in `explore`**: when the user selects a signal entry in `explore` (type tab = `signals`), the detail pane shows two sections: the local pins of that signal (module/part/pin labels), then — if `find_net(sys, module, signal)` returns ≥ 2 members — a `Net members (across connections)` section listing every `(module, signal, type)` reachable through `Connection::pin_map`. The signal-detail header includes `K net members across N module(s)` (or `INCONSISTENT` if `net_type_consistent` returns false). This is what replaced the former dedicated `net` screen.
+
+**Enter-to-edit matrix in `explore`** — `explore_detail_sig` stores a `module\tsignal` payload per detail row (empty = read-only). The detail-menu `on_enter` parses the `\t` and calls `OpenSignalTypeDialog(mod, sig)`, so Enter works correctly for peer-module rows. Today:
+
+| Focus              | parts                 | signals                          | connections |
+|--------------------|-----------------------|----------------------------------|-------------|
+| `children_menu`    | jump to set-connector-type screen pre-filled on this part (focus on type input) | open signal-type popup for the selected signal | — |
+| `detail_menu`      | open signal-type popup for the pin's signal (skipped on `(NC)`) | open signal-type popup for the row's `(module, signal)` — works for both local pins (= current signal) and cross-module net members | — |
+
+Module / type / filter focuses do not have an Enter binding.
 
 **Long-running scripts (`source`)**: `Source(file)` is event-paced. It reads all lines, sets `loading = true`, then spawns a detached pacing thread that posts `Event::Special("\x02tick")` every ~30 ms — **but only one tick at a time**: the main thread acks each one (`tick_in_flight = false` at the end of `ProcessNextSourceLine`) before the ticker sleeps and posts the next. Without this, FTXUI batches all queued events into one render pass; a long line (e.g. a heavy Mentor parse) would let the ticker queue many ticks and the modal would freeze. Each tick triggers `ProcessNextSourceLine`, which processes one effective line (skipping comments/blanks) via `Submit()`. A centred `borderDouble` modal (`" Computing… "` + filename + `N / M lines`) is overlaid via `dbox` while `loading` is true.