docs: bound params are overridable defaults — C12 amendment, glossary, guide

Task 7 of the bound-override cycle: the design ledger's C12 records the
bound-as-default semantics (axis 1 may name a bound param; identity reads
the authored document; the retired axes-bind-only-open-knobs restriction
was an implementation consequence, not a recorded decision), the glossary's
blueprint entry carries the same sentence, and the authoring-guide's
data-only starter section explains the one-file run+sweep quickstart.

closes #246

docs/authoring-guide.md

@@ -38,10 +38,11 @@ the same shape every node in `aura-std` already follows.
 - **The project's own signal doesn't need a crate by default.** `aura new`
   scaffolds a **data-only** project (`docs/project-layout.md`, "A project
   repo (two tiers)") — a strategy over the std vocabulary is a
-  blueprint/campaign document, not Rust: the scaffold ships a single closed
-  `signal.json` starter, runnable immediately with no build step, and also
-  the sweep target itself (a bound param is a default any `--axis` may
-  override, #246).
+  blueprint/campaign document, not Rust: the scaffold ships **one** closed
+  `signal.json` starter that serves both verbs — `aura run` uses its bound
+  values as-is, `aura sweep --axis <bp>.fast.length=2,4,8` overrides them
+  (bound = default, not fixed); `--list-axes` lists the open knobs and the
+  bound defaults alike, so every override target is discoverable.
 - **A project-specific *native* node type** — the moment §0's three-part
   pattern is actually needed — lives in an attached **node crate**:
   `aura nodes new <name>` scaffolds a sibling cdylib crate (`Cargo.toml` +