T08: give provisional defaults an owner, a date, and a visible age

Five scenarios encoded U-item defaults with no owner and no review date,
so they could shape the kernel indefinitely while looking handled.

Each now carries provisional_owner and provisional_raised, and the
runtime's ScenarioFile learned both fields (deny_unknown_fields meant
adding them to YAML alone would have failed every scenario -- the parser
had to agree).

make coverage reports every provisional item with its owner and age in
days, warns on any with no owner, and warns past 30 days. It WARNS
rather than breaking the build, on purpose: the ruling is ground-game's
to make and the kernel cannot make it for them. What the loop can
enforce is that evidence files list them, which is now stated in
GroundRules.

rule-coverage --self-test gained an assertion that every provisional
item has both fields, so the next one added without them fails a
command rather than passing quietly.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

crates/cb-game-runtime/src/scenario.rs

@@ -21,6 +21,16 @@ pub struct ScenarioFile {
     /// scenario, not the kernel.
     #[serde(default)]
     pub provisional: bool,
+    /// Who must rule on the U-item this scenario encodes. Required when
+    /// `provisional` is true: a provisional default with no owner can
+    /// shape the kernel indefinitely while looking handled
+    /// (CB-WP-0003 T08).
+    #[serde(default)]
+    pub provisional_owner: String,
+    /// ISO date the provisional default was raised, so its age is
+    /// reportable by `make coverage`.
+    #[serde(default)]
+    pub provisional_raised: String,
     pub seed: u64,
     pub setup: Setup,
     pub commands: Vec<CommandStep>,