refactor(aura-cli): retire the dead-end runs list/rank CLI surface

Since cycle 0045 the flat runs.jsonl store has had no producer (sweep/mc/
walkforward persist to the family store; `aura run` does not persist), so
`aura runs list` / `runs rank` read a store nothing populates — a live dead-end
surface, the honesty gap the Runway milestone closes.

Resolve the C18 deferred fork (INDEX.md) as (b) RETIRE: drop the two CLI commands
+ their dispatch arms, usage fragments, and the now-unused load_runs_or_exit.
Families (sweep/mc/walkforward, C21) subsume standalone over-time comparison. The
aura-registry flat lib API (append/load/rank_by/optimize) is RETAINED — optimize
backs walk-forward's in-sample step, rank_by backs `runs family ... rank`.
`runs families` / `runs family` are untouched.

Decision recorded on #73 (user-directed (b), 2026-06-18). Cosmetic sub-item
(json! family-wrapper -> to_json() stdout key-order unification) deferred to a
follow-up: json! routes the embedded report through serde_json::Value, which
re-alphabetizes keys, so it needs manual JSON construction, not a trivial swap.

RED-first: the retire test asserted `runs list`/`rank` now exit 2 (was exit 0).
Verified: cargo build --workspace, clippy --all-targets -D warnings, and
cargo test --workspace all green.

closes #73

crates/aura-cli/src/main.rs

@@ -683,28 +683,6 @@ fn mc_report() -> String {
     out
 }
 
-/// `aura runs list`: print every stored run record, in store (over-time) order.
-fn runs_list() {
-    for report in &load_runs_or_exit() {
-        println!("{}", report.to_json());
-    }
-}
-
-/// `aura runs rank <metric>`: print the stored runs best-first by `metric`.
-fn runs_rank(metric: &str) {
-    match rank_by(load_runs_or_exit(), metric) {
-        Ok(ranked) => {
-            for report in &ranked {
-                println!("{}", report.to_json());
-            }
-        }
-        Err(e) => {
-            eprintln!("aura: {e}");
-            std::process::exit(2);
-        }
-    }
-}
-
 /// `aura runs families`: one header line per stored family (id, kind, member
 /// count), in first-seen store order.
 fn runs_families() {
@@ -726,8 +704,7 @@ fn runs_families() {
 
 /// `aura runs family <id> [rank <metric>]`: list one family's member reports in
 /// ordinal order, or best-first by `metric`. An unknown id is an empty family
-/// (prints nothing, exit 0, consistent with `runs list` over an empty store); an
-/// unknown metric is a usage error (stderr + exit 2).
+/// (prints nothing, exit 0); an unknown metric is a usage error (stderr + exit 2).
 fn runs_family(id: &str, rank: Option<&str>) {
     let reg = default_registry();
     let members = match reg.load_family_members() {
@@ -756,14 +733,6 @@ fn runs_family(id: &str, rank: Option<&str>) {
     }
 }
 
-/// Load the registry or exit 2 with the error. A missing registry loads empty.
-fn load_runs_or_exit() -> Vec<RunReport> {
-    default_registry().load().unwrap_or_else(|e| {
-        eprintln!("aura: {e}");
-        std::process::exit(2);
-    })
-}
-
 // --- MACD proof-of-concept (a richer, nested indicator + strategy) -----------
 
 /// The MACD signal as a named composite: price → fast/slow `Ema` → the MACD line
@@ -887,7 +856,7 @@ fn run_macd() -> RunReport {
 }
 
 const USAGE: &str =
-    "usage: aura run [--macd] | aura run --real <SYMBOL> [--from <ms>] [--to <ms>] | aura graph | aura sweep [--name <n>] | aura mc [--name <n>] | aura walkforward [--name <n>] | aura runs list | aura runs rank <metric> | aura runs families | aura runs family <id> [rank <metric>]";
+    "usage: aura run [--macd] | aura run --real <SYMBOL> [--from <ms>] [--to <ms>] | aura graph | aura sweep [--name <n>] | aura mc [--name <n>] | aura walkforward [--name <n>] | aura runs families | aura runs family <id> [rank <metric>]";
 
 fn main() {
     // Collect argv and match the whole vector: every accepted form is exhaustive,
@@ -911,8 +880,6 @@ fn main() {
         ["walkforward", "--name", n] => run_walkforward(n),
         ["mc"] => run_mc("mc"),
         ["mc", "--name", n] => run_mc(n),
-        ["runs", "list"] => runs_list(),
-        ["runs", "rank", metric] => runs_rank(metric),
         ["runs", "families"] => runs_families(),
         ["runs", "family", id] => runs_family(id, None),
         ["runs", "family", id, "rank", metric] => runs_family(id, Some(metric)),