feat(preflop-charts): scenario-scoped charts, TUI viewer, and verify command

Rework the preflop chart system around (position, scenario) — each
`PositionCharts` holds one `PreflopChart` per scenario (rfi/vs_open/
vs_3bet/vs_4bet), replacing the labeled Raise/ThreeBet/FourBet scheme
that tried to pack every scenario into one strategy. `PreflopStrategy`
collapses to `{raise, call}` with fold implicit; both fields are
optional in JSON so the common `{"raise": 1.0}` case is terse. A new
`four_bet_plus_multiplier` (default 2.5) sizes 4-bet raises in Vs3Bet.

Adds `rsp arena charts` (interactive TUI hand-grid viewer with
auto-switching to a non-empty scenario when seats change) and
`rsp arena verify` with `--summary` for combo-weighted range stats per
position/scenario. The in-tree example config is rewritten in the new
format; a one-shot migration script for local configs lives outside
the tree.

Author: elliottneilclark

examples/configs/preflop_6max_rfi.json

@@ -274,7 +274,7 @@ pub enum AgentConfig {
 ///
 /// Can be either a preset name (e.g., "6max_gto", "tight", "loose")
 /// or an inline chart configuration.
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize)]
 #[serde(untagged)]
 #[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 pub enum PreflopChartConfigOption {
@@ -284,6 +284,26 @@ pub enum PreflopChartConfigOption {
     Inline(PreflopChartConfig),
 }
 
+// Custom Deserialize so failures on the inline path surface the *specific*
+// PreflopChartConfig parse error (e.g. "missing field `charts`", "unknown
+// field `position`") instead of serde's generic "data did not match any
+// variant of untagged enum" message, which is useless when debugging a
+// malformed config.
+impl<'de> Deserialize<'de> for PreflopChartConfigOption {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let value = serde_json::Value::deserialize(deserializer)?;
+        if let serde_json::Value::String(s) = &value {
+            return Ok(PreflopChartConfigOption::Preset(s.clone()));
+        }
+        serde_json::from_value::<PreflopChartConfig>(value)
+            .map(PreflopChartConfigOption::Inline)
+            .map_err(serde::de::Error::custom)
+    }
+}
+
 impl Default for PreflopChartConfigOption {
     fn default() -> Self {
         PreflopChartConfigOption::Preset("6max_gto".to_string())

src/arena/agent/config.rs

@@ -15,7 +15,7 @@ pub use configurable::{
     RoundActionConfig,
 };
 pub use preflop_chart::{
-    PreflopChartActionConfig, PreflopChartActionGenerator, PreflopChartConfig,
+    PositionCharts, PreflopChartActionConfig, PreflopChartActionGenerator, PreflopChartConfig,
     PreflopChartConfigError,
 };
 pub use simple::SimpleActionGenerator;