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>

doc/README.md

@@ -5,9 +5,11 @@ Auto-generated API reference and high-level design notes for the
 
 ## Layout
 
-- [`api/`](api/) — auto-generated API reference (Doxygen XML → custom
-  Markdown emitter). Browse classes and files directly in gitea's
-  Markdown renderer. Top page: [`api/index.md`](api/index.md).
+- [`user/`](user/) — **user-facing** docs (hand-written intro/tutorial
+  + auto-generated command reference). Start at [`user/index.md`](user/index.md).
+- [`api/`](api/) — **developer-facing** API reference (Doxygen XML →
+  custom Markdown emitter). Browse classes and files directly in
+  gitea's Markdown renderer. Top page: [`api/index.md`](api/index.md).
 - [`../DESIGN.md`](../DESIGN.md) — implementation notes: domain
   conventions, TUI flow, gotchas. Hand-maintained.
 - [`classes.puml`](classes.puml) — PlantUML class diagram for the
@@ -41,8 +43,14 @@ Pipeline:
 src/**/*.{hpp,cpp}  ──┐
 README.md            ─┼─► doxygen ─► build/doc/xml/  ─► gen_api_md.py ─► doc/api/
 DESIGN.md            ─┘            (Doxyfile.in)
+
+(built essim) ────────► essim --commands-md ──────────────────────────► doc/user/commands.md
 ```
 
+`doc/user/index.md` and `doc/user/scripting.md` are hand-written; only
+`doc/user/commands.md` is regenerated. The `doc` target depends on the
+`essim` binary so a stale build is rebuilt before the dump is taken.
+
 If either Doxygen or Python 3 is missing at CMake-configure time the
 `doc` target is silently disabled (the regular build still works) and a
 status line is emitted in the CMake log telling you which one to install.