feat: add GenesysCX study and fix Streamlit chart key collisions

- Add 202512_GenesysCX TEI study (config, seed data, notebooks, README)
  with NPV $10.8M / ROI 266% including AI-token cost line
- Add explicit `key` parameter to all chart wrappers in app/components
  to prevent StreamlitDuplicateElementId errors when the same figure
  type renders across Summary/Benefits/Costs tabs
- Render benefits bar and cost pie charts on their respective tabs
- Add benefits_vs_costs_by_year chart wrapper

studies/202512_GenesysCX/ctm-token-calculator/tokencalc/__init__.py

@@ -0,0 +1,77 @@
+"""
+tokencalc — Genesys AI token cost & business case calculator core.
+
+Pure-Python, UI-agnostic. The JupyterLab notebook and the Streamlit
+app are thin presentation layers over these functions.
+"""
+
+from .benefit_model import calculate_total_benefit
+from .business_case import build_business_case, npv, payback_years
+from .cost_model import (
+    calculate_consumption_ai_cost,
+    calculate_per_user_ai_cost,
+    calculate_platform_license_cost,
+    calculate_total_cost,
+)
+from .defaults import (
+    CONTRACTED_NAMED_USERS,
+    CTM_DEFAULT_FEATURE_SCOPES,
+    CTM_DEFAULT_ROLLOUT,
+    CTM_DEFAULT_SITES,
+    CTM_DEFAULT_TAKEOUTS,
+    DEFAULT_METERS,
+    DEFAULT_PRICING,
+    PLATFORM_RATE_PER_USER_MONTHLY,
+)
+from .rollout import NO_ROLLOUT, RolloutPlan
+from .exports import (
+    export_csv,
+    export_excel,
+    meters_dataframe,
+    scenario_state_from_json,
+    scenario_state_to_json,
+    sites_dataframe,
+)
+from .inputs import CostTakeout, FeatureScope, SiteInput
+from .meters import Confidence, MeterType, TokenMeter, TokenPricing
+from .scenarios import BENEFIT_PARAMS, SCENARIOS, Scenario, get_scenario
+
+__version__ = "0.1.0"
+
+__all__ = [
+    "BENEFIT_PARAMS",
+    "CONTRACTED_NAMED_USERS",
+    "CTM_DEFAULT_FEATURE_SCOPES",
+    "CTM_DEFAULT_ROLLOUT",
+    "CTM_DEFAULT_SITES",
+    "CTM_DEFAULT_TAKEOUTS",
+    "Confidence",
+    "CostTakeout",
+    "DEFAULT_METERS",
+    "DEFAULT_PRICING",
+    "FeatureScope",
+    "MeterType",
+    "NO_ROLLOUT",
+    "PLATFORM_RATE_PER_USER_MONTHLY",
+    "RolloutPlan",
+    "SCENARIOS",
+    "Scenario",
+    "SiteInput",
+    "TokenMeter",
+    "TokenPricing",
+    "build_business_case",
+    "calculate_consumption_ai_cost",
+    "calculate_per_user_ai_cost",
+    "calculate_platform_license_cost",
+    "calculate_total_benefit",
+    "calculate_total_cost",
+    "export_csv",
+    "export_excel",
+    "get_scenario",
+    "meters_dataframe",
+    "npv",
+    "payback_years",
+    "scenario_state_from_json",
+    "scenario_state_to_json",
+    "sites_dataframe",
+]