Dashboard + palette + analyze screen; consolidated categorization rules.

UI restructuring:

- Dashboard (`screen_dashboard.cpp`, `screen_idx = 6`) is the new home
  screen at boot. Reads Overview / Health / Analysis / Modules from
  the current System every frame; per-module rows list parts grouped
  by `connector_type` and a Power/Gnd inference summary (yellow when
  any name-Power signal is refuted). Scrollable via PgUp/PgDn/Home/End.
  Letter shortcuts: `c`=console, `s`=search, `p`=plug (alias of
  connect), `t`=set-type, `e`=explore, `n`=net, `a`=analyze, `q`=quit.
- Global Ctrl-P palette (`screen_palette.cpp`) — fuzzy-finds over
  registered commands + module / signal names. Activation runs the
  bare command or jumps to the matching screen with state seeded.
- Unified analyze screen (`screen_analyze.cpp`, `screen_idx = 7`):
  tabbed layout (`Issues / Groups / Types`), Tab or ←→ to switch
  tabs, ↑/↓ to navigate the focused list. Replaces the previous
  shell-bouncing `[v]erify` shortcut — `verify` content is now in
  the Issues tab. Types tab attaches the decision rationale to each
  signal row (fan-out / voltage / hard floor).
- Context help panel: `RenderHelpPanel(title, entries)` in
  `tui_helpers.{hpp,cpp}` rendered on the right of every screen.
- Console (former "log") rename: screen 0 is `[c]onsole` in the UI
  and "console" in its help-panel title. The underlying screen and
  the shell prompt are unchanged.
- Esc from any non-home screen returns to the dashboard. The
  dashboard itself swallows Esc; quit via `q` / the `quit` command.
  `quit` now calls `screen_ptr->Exit()` directly so it works from
  any screen including via the palette.

Signal type inference:

- `Signal::type` defaults to `Other` — auto-inference no longer
  happens at construction.
- `infer_signal_types(System*)` is called at the end of every load.
  Three rules: GndShield from name alone; Power requires name match
  + a hard fan-out floor (< 3 pins = always Other, regardless of
  name or voltage) + at least one positive structural signal
  (fan-out ≥ 4 OR voltage pattern in the name like `3V3`, `5V`).
- Thresholds exposed in `analysis.hpp` (`POWER_FANOUT_HARD_FLOOR`,
  `POWER_FANOUT_CONFIRM_MIN`, `has_voltage_pattern`) so the analyze
  screen can render the same rationale without duplicating logic.
- `set-signal-type` still wins; save/restore round-trips the type.

Analysis groups & anomalies:

- New `GroupKind::DiffBus` — ≥ 2 diff pairs sharing the same
  outer-stem with consecutive integer indices are aggregated into a
  single bus (`MDI[0..3]_P/N`). `MDI0` and `PCIE_TX_0` index forms
  both accepted. Solo pairs under a bus-able stem fall back to
  `DiffPair`.
- New `AnomalyKind::DiffBusGap` for missing lanes.

Documentation:

- `DESIGN.md`: dedicated "Categorization rules (normative)" section
  consolidating signal type, NC origin, signal groups, anomalies,
  component kind, and connector wiring rules with exact thresholds
  and decision order.
- `doc/user/analysis.md` (new): user-facing version of the same
  rules in plain language. Linked from `doc/user/index.md`.

Tests: +6 new cases (62 total). Adjusted `test_persist.cpp` to set
the signal type explicitly in the fixture (no more auto-inference).

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

tests/test_persist.cpp

@@ -98,15 +98,17 @@ TEST_CASE("save+restore round-trip preserves modules, parts, types, signals, NC"
 }
 
 TEST_CASE("save+restore preserves signal type overrides") {
+    // The Signal ctor defaults to Other; promotion to Power/Gnd is the job
+    // of `infer_signal_types(sys)` at load time. Here we just set the types
+    // explicitly to assert that save/restore round-trips them.
     auto sys = make_fixture();
-    // Force a non-default override on a signal that auto-infers as Other.
     Signal *vcc = sys->modules()->get("BKP")->signals->get("VCC");
     REQUIRE(vcc);
-    CHECK(vcc->type == SignalType::Power);  // auto-detected from "VCC"
+    vcc->type = SignalType::Power;
 
     Signal *gnd = sys->modules()->get("BKP")->signals->get("GND");
     REQUIRE(gnd);
-    CHECK(gnd->type == SignalType::GndShield);
+    gnd->type = SignalType::GndShield;
 
     std::string path = tmp_path("essim_signal_type.txt");
     std::string err;