Model Current Game Mode and the other value reads Bastion makes #105

Problem

After #103, Bastion on athena main (docs/scenario-examples/valid/bastion.json plus buttons for every slot on both players) runs rule 187 to its Wait and then ends not_modeled at tick 0:

{ "status": "not_modeled", "construct": "value getCurrentGamemode", "tick": 0,
  "location": { "rule": 188, "name": "[Bastion] Restart active match", "condition": 0 } }

Each unmodeled value costs a full cycle. #103 handled actions as a class; this issue does the same for the value reads Bastion makes.

Scope

1. Current Game Mode (getCurrentGamemode): the game mode is a scenario fact the simulator cannot derive (the catalog records no map-to-mode mapping). Add an optional top-level scenario field (name it after the catalog read, e.g. gameMode, taking catalog Game Mode member ids) with the absent-input rule: absent gives missing_input named for the field; an unknown id is rejected at load; no default. Add it to docs/scenario-examples/valid/bastion.json with a mode the workload can run in.
2. Audit every other value that bastion.ow reads and athena does not yet model (AST-walk the workload and compare with the evaluator's supported list, as Model presentation-only and game-mode actions as no-ops (Disable Inspector Recording and class) #103 did for actions). For each, classify with the catalog description:
   • Scenario fact (cannot be derived from the program or scenario today, for example Match Time, a player's Health, Is Dead, Number Of Players): add a scenario input with the absent-input rule, or, if it needs a model of state that other actions mutate (health pools, life state, roster, match clock), keep it not_modeled and list it in the PR body together with the category-2 actions that mutate it (the list in the Model presentation-only and game-mode actions as no-ops (Disable Inspector Recording and class) #103 PR body), so one follow-up issue per state family can design it.
   • Derivable from state athena already tracks: implement it.
   • Do not guess; if the catalog text does not settle a case, keep it not_modeled and list it.
3. Docs: docs/scenario-format.md (field table, modeled reads, missing inputs), schema file, docs/simulator-interface.md, docs/findings.md for modeled-not-measured choices; the committed bastion.json example must include buttons for every slot Bastion reads (the Model presentation-only and game-mode actions as no-ops (Disable Inspector Recording and class) #103 PR reported it does not, and the run stops at button.reload, p2, rule 93, so fix the example), slot and matchPhase.

Acceptance

• Tests for each new input: present, absent (missing_input naming the field), unknown value rejected; each newly derived value.
• Bastion rerun with the committed bastion.json unchanged except what this PR adds: report the new first stop, or completion, and the remaining unmodeled values grouped by state family. Parent: Run Bastion to completion on athena-sim #45.