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/authoring-guide.md

@@ -31,7 +31,7 @@ $ aura graph build < smacross.json > blueprint.json
 Nodes are referenced by an **identifier** (given by `add`, see below); ports
 are dotted `<identifier>.<port>` on both sides of a wire.
 
-### The six ops
+### The seven ops
 
 | op | JSON shape | does |
 |---|---|---|
@@ -41,6 +41,7 @@ are dotted `<identifier>.<port>` on both sides of a wire.
 | `feed` | `{"op":"feed","role":<str>,"into":[<port>, …]}` | fan a previously-declared role into one or more interior input slots, all-or-nothing (a failing target leaves none of the batch wired). |
 | `connect` | `{"op":"connect","from":<port>,"to":<port>}` | wire one interior output field to one interior input slot. A `connect` that would close a dataflow cycle is rejected immediately — the only legal feedback path is an explicit delay/state node (domain invariant 5). |
 | `expose` | `{"op":"expose","from":<port>,"as":<str>}` | promote an interior output field to a boundary output under the alias `as` — the only op whose name key is a real *alias* (contrast `add`'s `name`, which is an identifier, not a rename). |
+| `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 typed-tag representations used everywhere in this
 family of artifacts:
@@ -78,6 +79,12 @@ up in `--params`/`--list-axes`, and no campaign axis and no `aura sweep
 --axis` can reopen it. `bind` is for a constant the strategy never varies;
 leave a param unbound, as all three are here, to keep it open for sweeping.
 
+A param therefore has three states: **open** (a sweepable axis), **bound**
+(closed by a `bind` — gone from the axis namespace), and **ganged** (open, but
+fused with its siblings under ONE public knob declared by a `gang` op; the
+member addresses are unbindable and only the gang's own single-segment name —
+wrapped like any knob, e.g. `graph.channel_length` — appears in `--list-axes`).
+
 ### Commands
 
 ```
@@ -125,6 +132,10 @@ raw   (--params, campaign axes):  fast.length
 wrapped (--list-axes, --axis):    graph.fast.length
 ```
 
+A ganged knob's raw address has one path segment less than a member address
+would — it sits at the composite's own level, like a role name (e.g.
+`channel_length`, not `channel_hi.length`) — and wraps identically (`graph.channel_length`).
+
 `--content-id`, `--identity-id`, `--params`, and `graph register` all accept
 **either** shape: the raw op-script array or an already-built `#155`
 blueprint envelope (object) — shape-discriminated automatically, so you