feat(0091): byte-canonical blueprint emit; record the equality-surface decision

#164 — tighten the C24 "canonical, versioned" blueprint contract on two corners
the milestone fieldtest surfaced. Both forks were derivable; resolved with
rationale (recorded on #164).

Fork 1 — canonical artifact carries no trailing newline. `blueprint_to_json`
returns the JSON value with no trailing newline (647 bytes for the SMA-cross
fixture); `aura graph build` had framed it with a `println!` (648). The library
serializer is the single canonical source — the form content-addressed topology
identity (#158) hashes — so the CLI is a transport that must not mutate the
bytes: `build_cmd` now `print!`s the canonical bytes verbatim, making the CLI and
library emit paths byte-identical. RED-first: the new E2E
`graph_build_emit_is_byte_canonical_no_trailing_newline` pinned the trailing
newline (FAIL), green after the one-line change. The two cycle-0088 `.out.json`
goldens are re-recorded at 647 bytes. The loader stays lenient (a trailing
newline on input still parses, Tier-1 robustness; the milestone fieldtest's
`mt_4` tolerance check is unaffected).

Fork 2 — the canonical JSON is the blueprint equality/identity surface; no
second in-memory PartialEq/Debug is added. `Composite`/`BlueprintNode` cannot
derive them: `PrimitiveBuilder` (aura-core node.rs) holds a
`build: Box<dyn Fn(&[Cell]) -> Box<dyn Node>>` closure, neither comparable nor
printable. Equality could only be defined over the serialized data, of which
`blueprint_to_json` is already the single source; a separate in-memory equality
notion would be a redundant second source of truth and a drift hazard against
the form #158 hashes. Recorded the decision (discharges acceptance box 2's "or
JSON-string is the intended equality surface" arm) in the C24 ledger; no code
added for it.

Verified: cargo test --workspace green (51 suites, incl. the new RED->green E2E);
cargo clippy --workspace --all-targets -D warnings clean.

closes #164

crates/aura-cli/src/graph_construct.rs

@@ -132,7 +132,11 @@ pub fn build_cmd() {
         std::process::exit(2);
     }
     match build_from_str(&doc) {
-        Ok(json) => println!("{json}"),
+        // `print!`, not `println!`: the canonical artifact is exactly the library
+        // `blueprint_to_json` bytes (the form #158 content-addresses) — a JSON value
+        // with no trailing newline. The CLI is a transport; it must not frame the
+        // canonical bytes (#164).
+        Ok(json) => print!("{json}"),
         Err(msg) => {
             eprintln!("aura: {msg}");
             std::process::exit(2);