feat(cli, std, research): self-describing surfaces — two-layer help, per-entry meanings, op reference

The binary is the only always-present teacher (C29); the 2026-07-22 external
field test showed the help teaching nothing but the verb inventory. This
cycle makes every closed vocabulary the binary ships listable with a one-line
meaning, and opens the help with the concepts the field agent had to discover
forensically.

#315 — help + introspection:
- `aura --help` opens with the two-layer concepts paragraph (research verbs
  as sugar over registered process/campaign documents; the directly
  authorable data plane; bias-as-target-position + protective-stop execution
  model in R; how traces come to exist).
- Each document-bridged sugar verb's long help names the process shape it
  desugars to (sweep -> std::sweep; walkforward -> [std::grid,
  std::walk_forward]; mc -> + std::monte_carlo; generalize -> [std::sweep
  (selection), std::generalize]). `run` is not verb_sugar-bridged, so its
  help points at the canonical document-first form instead of claiming a
  desugaring it does not perform.
- `graph introspect --vocabulary` lists each node type with its schema doc
  (bare names taught nothing); `--node <T>`'s head line carries the meaning.
- `graph introspect --folds` (new): the tap-fold vocabulary with bind rule,
  output kind, and meaning — it existed only as source comments. The rows
  live in aura-std (`fold_vocabulary`), unit-pinned against
  `fold_binds_at`/`fold_output_kind` so the prose cannot drift from the
  executable rules, and doc_gate-checked (C29 entry seam). The discovery
  surface is graph introspect because folds bind at graph-declared taps
  (C27); the document layer still refuses a folds slot pending #310.
- `process introspect --metrics` lines carry each metric's meaning (the doc
  column existed since #316 but was never printed).
- `campaign introspect --block std::presentation` lists the four persisted
  taps' meanings under the persist_taps slot.
- The scaffolded project CLAUDE.md teaches the execution semantics (bias as
  held target, protective stop, R) and the document data plane.

#323 — C29 authoring surfaces:
- `introspect --unwired` enumerates the optional `description` envelope slot
  for both document kinds (absent-only, like risk/cost); the campaign lib
  fixture gains a description, and the risk/cost-bound e2e binds description
  too so "no open slots" keeps meaning complete.
- `graph build --help` carries the op-list reference: all nine op kinds with
  fields and a worked element each (OP_REFERENCE lives beside OpDoc so a new
  variant is one screen from its help line).
- The authoring guide's S0 worked literal is byte-pinned to the scaffold's
  LIB_RS template (rendered with the guide's my_lab namespace); the scaffold
  e2es compile that template for real, so the pin is a transitive compile
  guard. The template gains the guide's C29 comment, the guide gains the
  template's rename note — one worked example, two surfaces, zero drift.

Deliberately out of scope (ratified #319, 2026-07-24): no doc-strings for
the quintet's 48 flag fields — the sugar surface retires; only the pointer
lines above bridge toward the document layer.

Verification: full workspace suite green, clippy -D warnings clean,
aura-bench exit 0 with all fingerprints OK (help_ms +1.6% — the longer help
text, in tolerance), cargo doc warning count unchanged (7 pre-existing).
9 new e2e pins in tests/help_self_description.rs; guide + CLAUDE.md pins in
scaffold unit tests; fold-vocabulary rules + doc_gate unit-pinned in
aura-std.

closes #315
closes #323

docs/authoring-guide.md

@@ -122,7 +122,8 @@ impl Scale {
     pub fn new(factor: f64) -> Self {
         Self { factor, out: [Cell::from_f64(0.0)] }
     }
-
+    // Replace `doc` below when renaming this sample node — it must keep
+    // describing the node's own behaviour, not this scaffolding step.
     pub fn builder() -> PrimitiveBuilder {
         PrimitiveBuilder::new(
             "my_lab::Scale",