feat(aura-cli): aura runs registry — persist on sweep, list + rank (cycle D / iter 3)

Final iteration of the run-registry cycle (#33): the read surface that makes a
sweep family — and runs across separate invocations — comparable over time
(C18's "compare experiments over time", which has no home in git or Gitea).

- `aura sweep` now persists each point's RunReport to runs/runs.jsonl (append-
  only, one serde_json line per run) in addition to printing it.
- `aura runs list` prints every stored record, in store order.
- `aura runs rank <metric>` prints the stored runs best-first by the metric
  (total_pips desc; max_drawdown / exposure_sign_flips asc); an unknown metric
  is a usage error (exit 2), like every other aura arg error.

sweep_report splits into a production sweep_family() (the pure run) and a
#[cfg(test)] renderer kept for the in-bin goldens; the dispatch gains run_sweep
/ runs_list / runs_rank over default_registry() (runs/runs.jsonl under cwd).
Process goldens run the binary in a temp cwd so persistence never dirties the
repo; /runs/ is git-ignored as a backstop.

Verified end-to-end: two `aura sweep` invocations accumulate 8 records;
`aura runs list` shows all 8; `aura runs rank total_pips` orders them best-first;
`aura runs rank bogus` exits 2 with the known-metrics hint. cargo test
--workspace green (cli_run 11, registry 5, engine 93, …); clippy
--workspace --all-targets -D warnings clean; no stray runs/ in the work tree.

refs #33

crates/aura-cli/Cargo.toml

@@ -12,4 +12,5 @@ path = "src/main.rs"
 [dependencies]
 aura-core = { path = "../aura-core" }
 aura-engine = { path = "../aura-engine" }
+aura-registry = { path = "../aura-registry" }
 aura-std = { path = "../aura-std" }