Migrate Amazon Connect TEI study to the Mercury Notebook Pattern

studies/202602_AmazonConnect -> studies/202602_TEI_Amazon_Connect,
rebuilt as pattern Variant 4 (TEI composite reproduction):

- teicalc/ self-contained engine (stdlib-only): Forrester's tables as
  the never-edited verbatim anchor, NPV/ROI/payback + risk adjustment
  transplanted from core/calculations, ClientDrivers overlay (contacts/
  agents/fixed driver map, growth re-base, identity at composite scale),
  scenario stress with core-identical semantics
- one deliverable notebook (business_case.ipynb): widget-pair sidebar
  drivers, published-vs-overlay KPI columns, cash-flow/waterfall/scenario
  charts, verification gate, backstage JSON data appendix
- gate + tests reproduce the published totals within PDF rounding:
  NPV $78.7M / ROI 342% / payback <6 months (engine $78,713,492 /
  342.48% / 0.7 months); 27 study tests, headless nbconvert green,
  stage simulation leak-free, exports carry the appendix
- old Athena workflow (00_provision..04_export, config.py, seed_data.py)
  deleted; git history preserves it; root test fixture repointed to
  teicalc.anchor
- docs: study README rewritten; root README points new studies at
  template/MercuryNotebook; pattern doc stale ctm-token-calculator paths
  now cite studies/202607_CTM_GenesysCX; Variant 4 cites this study as
  its realized reference

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

studies/202602_TEI_Amazon_Connect/teicalc/__init__.py

@@ -0,0 +1,56 @@
+"""
+teicalc — self-contained engine for the Amazon Connect TEI study
+(Forrester, February 2026). Mercury Notebook Pattern, Variant 4:
+verbatim composite anchor → published-totals gate → client overlay.
+"""
+
+from .anchor import ASSUMPTIONS, BENEFITS_VERBATIM, COSTS_VERBATIM, PUBLISHED
+from .model import (
+    X_LABELS,
+    YEAR_INDEX,
+    YEARS,
+    benefits_by_year,
+    by_calendar,
+    compute_summary,
+    costs_by_year,
+    discount_factor,
+    html_money,
+    initial_costs,
+    money,
+    month_label,
+    npv,
+    payback_label,
+    payback_months,
+    payback_years,
+    present_value,
+    risk_adjust_benefit,
+    risk_adjust_cost,
+    risk_adjusted_rows,
+    roi_pct,
+)
+from .overlay import (
+    BENEFIT_DRIVERS,
+    COMPOSITE,
+    COST_DRIVERS,
+    ClientDrivers,
+    growth_multiplier,
+    overlay_rows,
+    scale_factor,
+)
+from .scenarios import SCENARIOS, apply_scenario
+
+__version__ = "0.1.0"
+
+__all__ = [
+    "ASSUMPTIONS", "BENEFITS_VERBATIM", "COSTS_VERBATIM", "PUBLISHED",
+    "YEARS", "YEAR_INDEX", "X_LABELS",
+    "by_calendar", "month_label",
+    "discount_factor", "present_value", "npv", "roi_pct",
+    "payback_years", "payback_months", "payback_label",
+    "risk_adjust_benefit", "risk_adjust_cost", "risk_adjusted_rows",
+    "benefits_by_year", "costs_by_year", "initial_costs",
+    "compute_summary", "money", "html_money",
+    "ClientDrivers", "COMPOSITE", "BENEFIT_DRIVERS", "COST_DRIVERS",
+    "scale_factor", "growth_multiplier", "overlay_rows",
+    "SCENARIOS", "apply_scenario",
+]