fix: load_family resolves the enumerated family name, refusing ambiguity (#298)

GREEN for 78e68e6's RED. aura_runner::reproduce::load_family resolved
only the derived C18 handle '{family}-{run}' while the registry's
enumeration exposes the bare name factor — the natural
list-then-reproduce library workflow dead-ended (found by the #295
fieldtest; predates the extraction byte-identically). Resolution now:
exact-handle match keeps first precedence; a bare name naming exactly
one stored run resolves as fallback; an ambiguous name (several runs,
or a name/handle collision) refuses without guessing, listing the
candidate handles. Two additional tests pin the ambiguity refusal and
the handle-precedence-on-collision semantics.

Ledger record-reality rider: the C18 #158 paragraph claimed reproduce
refuses an unknown id with exit 2; the code has always exited 1 —
correct per C14's partition (the id names missing recorded state, a
runtime failure, not a usage error). The paragraph now records the
actual behaviour and the new name-fallback semantics.

Verification: cargo test --workspace green (1477 passed, 0 failed);
clippy --workspace --all-targets -D warnings clean.

closes #298

docs/design/INDEX.md

@@ -1512,7 +1512,12 @@ the integrity check). `aura reproduce <family-id>` re-derives every persisted me
 the member's blueprint by its `topology_hash`, reconstruct the sweep point from the
 recorded params, re-run through the **same** `run_blueprint_member` the live sweep uses
 (so bit-identity is by construction, C1), and compare metrics — refuse-don't-guess on an
-unknown id / missing stored blueprint (exit 2), DIVERGED → exit 1. The manifest + the
+unknown id / missing stored blueprint (exit 1 — recorded state is missing, C14's
+runtime-failure class; this paragraph over-claimed exit 2 until #298 recorded the code's
+actual, C14-consistent behaviour), DIVERGED → exit 1. The id resolves first as the
+derived `{family}-{run}` handle; a bare enumeration name naming exactly one stored run
+resolves as fallback, an ambiguous name refuses listing the candidate handles (#298 —
+the list-then-reproduce seam). The manifest + the
 content-addressed store + the commit are the complete re-derivation recipe (C18). One
 blueprint is stored per family (all members share the signal `topology_hash` — C11/C12
 dedup). `aura graph introspect --content-id` exposes the same id for an op-script, via the