Signal-type popup, NC pin tagging, interactive viewer hygiene.

- Enter on a signal entry (net / explore) opens a modal popup to pick
  power / gnd / other. Recording is deduped: a sequence of toggles on
  the same signal collapses to a single `set-signal-type` line; no-op
  selections record nothing.
- Bare interactive commands (the ones that open a full-screen mode)
  are no longer recorded by `script-save`. Their inline forms still
  are. Mutating actions inside a screen record their own canonical
  line.
- Mentor importer treats signals whose name starts with `unconnected`
  as no-connect — the pin is kept on the part without a signal and
  tagged `ImportedUnconnected`.
- `drop_singleton_signals` runs at the end of `load`: any signal with
  exactly one pin is detached (singletons are NC by definition); the
  pin is tagged `DroppedSingleton`. Count is reported inline.
- `verify` gains a one-line orphan summary (imported NC / dropped
  singleton totals). Pins materialised by `FillIdentityNCs` are
  excluded via a `pin_map` filter — they are bridged to a real signal
  on the peer module and are not real NCs at system level.
- NcOrigin tag is serialized in save snapshots as an optional 4th
  field on N records (backward-compatible).

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

src/tui/tui_helpers.cpp

@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <cctype>
 
+
 std::string ToLower(std::string s) {
     std::transform(s.begin(), s.end(), s.begin(),
                    [](unsigned char c) { return std::tolower(c); });