T08 iter 1: scenario runner executes; GROUND setup and Select step

Replaces the RunOutcome::Unimplemented stub with a real runner:

- ScenarioGame trait: games own setup presets and the command
  vocabulary, the runner owns execution, assertions, and determinism.
- K8 double-run: every scenario runs twice on the same seed and fails
  on state-hash divergence.
- K4/K11: applied events go through Envelope into EventLog, so seq
  monotonicity is enforced on the real path, not just in unit tests.
- setup.patch was parsed and silently dropped; the runner now applies
  it generically and errors on a path that does not exist, so a typo
  in a scenario can never pass as a no-op.
- Assertions: dot-path state lookup over objects and arrays, ordered
  event subsequence matching by field subset, exact rejects-set match.

GROUND rules realized: GR-S01..S04 setup (seeded shuffle, deal, Lead,
Surface Problem face up), GR-R02 Select commit, GR-R03 stress gate and
Freedom spend, GR-A13 targeting legality.

cb-sim dispatches by the scenario's game prefix and reports rule
coverage. 3 scenarios pass, 7 rules covered; fmt/clippy/tests green.

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

scenarios/ground/gr-r02-select.yaml

@@ -0,0 +1,35 @@
+scenario: ground/gr-r02-select
+description: >
+  Select step: each player commits exactly one face-down Action, and a
+  second commit from the same player is rejected as a duplicate.
+covers: [GR-R02, GR-A13]
+provisional: false
+seed: 42
+setup:
+  players: 3
+  preset: standard-3p
+commands:
+  - actor: P1
+    cmd: select_action
+    args: { action: ATTACK, target: P2 }
+  - actor: P2
+    cmd: select_action
+    args: { action: SUPPORT, target: P3 }
+  - actor: P3
+    cmd: select_action
+    args: { action: INVESTIGATE, problem: 2 }
+  # GR-R02: one selection per player per round.
+  - actor: P1
+    cmd: select_action
+    args: { action: GROUND }
+expect:
+  events:
+    - kind: ActionSelected
+      player: 0
+    - kind: ActionSelected
+      player: 1
+  state:
+    "selections.0.action": Attack
+    "selections.1.action": Support
+    "selections.2.problem": 2
+  rejects: [3]

scenarios/ground/gr-r03-stress-gate.yaml

@@ -0,0 +1,34 @@
+scenario: ground/gr-r03-stress-gate
+description: >
+  Stress gate: at Stress 4 only ATTACK or GROUND may be selected, until
+  the READY Freedom token is spent, which admits any one Action.
+covers: [GR-R03, GR-F03]
+provisional: false
+seed: 42
+setup:
+  players: 3
+  preset: standard-3p
+  patch:
+    "players.0.stress": 4
+commands:
+  # Gated: SUPPORT is not admitted at Stress 4.
+  - actor: P1
+    cmd: select_action
+    args: { action: SUPPORT, target: P2 }
+  - actor: P1
+    cmd: spend_freedom
+  # The same Action is now legal, and the token reads SPENT.
+  - actor: P1
+    cmd: select_action
+    args: { action: SUPPORT, target: P2 }
+expect:
+  events:
+    - kind: FreedomSpent
+      player: 0
+    - kind: ActionSelected
+      player: 0
+  state:
+    "players.0.stress": 4
+    "players.0.freedom_ready": false
+    "selections.0.action": Support
+  rejects: [0]