feat(cli,docs): ship the ganged open examples + document the gang construct (#61 tasks 7-8)

The two open examples now expose their author-intended single knobs — the
closed builders always bound these pairs to one value by hand; the open forms
falsely offered them as independent axes:
- r_breakout_open: channel_hi.length + channel_lo.length -> channel_length
  (the Donchian channel is structurally ONE parameter)
- r_meanrev_open: mean_window.length + var_window.length -> window; the band
  factor stays an independent axis
Regenerated via the emitters (never hand-edited); the closed examples are
byte-unchanged. The carve builders gang in the open branch only.

Test migration: the two axis-namespace pins, five --real e2e invocations
(single gang axis, the 10,20 diagonal for the campaign pair — the mismatched
20,40/10,20 grid was exactly the configuration space the gang retires), and
the param_stability row counts (4 -> 3). The r-sma walkforward golden anchor
is untouched (it never swept a ganged pair).

Docs: authoring-guide gains the seventh op + the third param state
(open/bound/ganged) + the gang wrap note; README op list + Axis concept;
glossary gang entry; ledger C24 records the gang verb and the pre-ship
Tier-2 dormancy (no format-version bump while no out-of-repo reader exists).

Verified: full workspace suite 1104/0 (--real e2e included, local data
present), clippy -D warnings clean, cargo doc clean; live acceptance:
introspect --params prints channel_length:I64 alone / window:I64 +
band.factor:F64.

closes #61

docs/design/INDEX.md

@@ -2093,6 +2093,11 @@ node type, edge semantics, or structural-axis kind) bumps `format_version` so an
 old reader refuses cleanly (`LoadError::UnsupportedVersion` / `UnknownNodeType`,
 already green). The per-section required-flag scheme is deferred (no current
 Tier-2 section to validate it; recorded on #156).
+Pre-ship dormancy (#61, 2026-07-10): until the first external ship there are
+no out-of-repo readers — reader and writer change atomically in one commit —
+so the Tier-2 bump discipline is dormant and structurally-semantic additions
+(the `gangs` section) land as additive-optional fields of v1; the first ship
+consciously freezes v1, gangs included, and activates the bump discipline.
 **Milestone delivered — 2026-06-30, cycle 0090 — the serializable format + loader + construction service.** A green end-to-end milestone fieldtest (`fieldtests/milestone-topology-as-data/`) proves the full author → serialize → load → construct → introspect → reproduce story from the public surface alone, 0 behavioural bugs; the round-trippable format (#155), the construction service (#157), and the forward-compat two-tier discipline (#156) all shipped. Polish filed forward: op-script grammar docs + a stale example (#163), the canonical trailing-newline / `Composite` value ergonomics (#164), CLI discoverability of `build`/`introspect` (#159).
 **Realization (2026-06-30, cycle 0092 — runs are built FROM blueprint-data, #165).**
 `aura run <blueprint.json>` now loads a serialized **signal** blueprint
@@ -2195,7 +2200,7 @@ fixture from the scaffolder.
 **Op-script grammar (`aura graph build`, the #157 wire surface).** The construction
 op-script is a JSON **array of ops**, each object internally tagged by `"op"`,
 replayed in order; nodes are referenced **by identifier**, ports as dotted
-`<identifier>.<port>`. The six verbs:
+`<identifier>.<port>`. The seven verbs:
 - `source` — `{"op":"source","role":<str>,"kind":<ScalarKind>}` — declare a root
   source role producing a base column of `kind`.
 - `input` — `{"op":"input","role":<str>}` — declare a root input role (kind inferred
@@ -2212,6 +2217,11 @@ replayed in order; nodes are referenced **by identifier**, ports as dotted
 - `expose` — `{"op":"expose","from":<port>,"as":<str>}` — promote an interior output
   field to a boundary output, aliased by `as` — **the only verb that keeps `as`**
   (a real alias, not a naming; contrast `add`'s `name`).
+- `gang` — `{"op":"gang","as":"channel_length","into":["channel_hi.length","channel_lo.length"]}`
+  — fuse two or more sibling params into ONE public knob: the member addresses
+  leave the sweepable param space and `as` replaces them; the bound or swept
+  value fans out to every member at bootstrap. Members must share one scalar
+  kind and stay open (un-bound).
 
 Value forms are the #155 representations: a `Scalar` bind value is the typed tag form
 `{"I64":2}` / `{"F64":0.5}` / `{"Bool":true}` / `{"Timestamp":<i64>}`, and `kind` is