User-facing docs: --commands-md flag, doc/user/ tree, anonymised script.

- `essim --commands-md [file]` instantiates the Tui, calls
  `Tui::DumpCommandsMd(ostream&)` which iterates the live registry and
  emits Markdown grouped by interactive/other, then exits. Single
  source of truth: a new `CommandSpec` field surfaces automatically.
- CMake `doc` target now `DEPENDS essim` and chains:
    doxygen → gen_api_md.py → doc/api/
    essim --commands-md      → doc/user/commands.md
- `doc/user/` adds:
    - index.md (hand-written) — first session, interactive-screen
      conventions, save/restore/replay overview.
    - scripting.md (hand-written) — `set`/`$var` expansion semantics,
      `source` event-paced execution, script-save denylist, worked
      example pointing at test/system.essim.
    - commands.md (auto-generated, regenerated by the `doc` target).
- Top-level README refocused on quick start; pointers to the new
  doc tree (user/, api/, DESIGN.md) instead of an inline command table.
- doc/README.md and DESIGN.md document the two-pipeline doc workflow.
- `test/system.essim` and user docs anonymised: bkp → backplane,
  vdn1/2/3 → payload1/2/3, cb3p → payload4, bpb/cob/ssu →
  peripheral1/2/3; netlist file names + variable names + paths all
  replaced with generic equivalents.

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

src/tui/shell.cpp

@@ -6,6 +6,7 @@
 #include <cstdlib>
 #include <filesystem>
 #include <fstream>
+#include <ostream>
 #include <set>
 #include <system_error>
 #include <thread>
@@ -289,6 +290,76 @@ void Tui::ProcessNextSourceLine() {
     in_source = loading_prev_in_source;
 }
 
+void Tui::DumpCommandsMd(std::ostream &out) const {
+    out << "# essim — command reference\n\n"
+           "Auto-generated from the live command registry. Regenerate with\n"
+           "`cmake --build build --target doc` after adding or changing\n"
+           "commands; the binary itself is the single source of truth.\n\n"
+           "Keys global to the shell: `Esc` cancels a multi-step prompt or\n"
+           "leaves an interactive screen; `Tab` completes commands/paths\n"
+           "(top-level prompt) or cycles focus inside an interactive\n"
+           "screen; `PageUp` / `PageDown` scroll output by 10 lines,\n"
+           "`Home` / `End` jump to top / bottom; ↑ / ↓ walk command\n"
+           "history.\n";
+
+    auto emit_group = [&](const std::string &title, bool want_interactive) {
+        bool printed_title = false;
+        for (const auto &kv : commands) {
+            const CommandSpec &spec = kv.second;
+            if (spec.interactive != want_interactive) continue;
+            if (!printed_title) {
+                out << "\n## " << title << "\n\n";
+                printed_title = true;
+            }
+            out << "### `" << kv.first << "`";
+            if (spec.interactive) out << "  *(interactive)*";
+            out << "\n\n" << spec.description << "\n\n";
+
+            if (spec.params.empty()) {
+                out << "**No arguments.**";
+            } else {
+                out << "**Arguments**\n\n";
+                int i = 1;
+                for (const auto &p : spec.params) {
+                    out << i << ". `" << p.name << "`";
+                    switch (p.completion) {
+                        case Completion::Path:    out << "  *(Tab → path completion)*"; break;
+                        case Completion::Command: out << "  *(Tab → command completion)*"; break;
+                        case Completion::None:    break;
+                    }
+                    out << "\n";
+                    ++i;
+                }
+            }
+            out << "\n";
+
+            std::vector<std::string> notes;
+            if (spec.interactive) {
+                notes.emplace_back("bare form opens an interactive screen; "
+                                   "inline form (all args) is scriptable");
+            } else if (!spec.prompt_for_missing) {
+                notes.emplace_back("no per-arg prompt: pass all args inline "
+                                   "(or run bare for an empty-args path)");
+            } else if (!spec.params.empty()) {
+                notes.emplace_back("missing args trigger one prompt each");
+            }
+            if (!spec.scriptable) {
+                notes.emplace_back("not recorded by `script-save` and "
+                                   "rejected by `source`");
+            }
+            if (!notes.empty()) {
+                out << "**Notes**\n\n";
+                for (const auto &n : notes) out << "- " << n << "\n";
+                out << "\n";
+            }
+            out << "---\n";
+        }
+    };
+
+    emit_group("Interactive commands", true);
+    emit_group("Other commands", false);
+}
+
 void Tui::AppendHistory(const std::string &cmd) {
     auto p = HistoryPath();
     if (p.empty()) return;