Migrate Genesys CX Cloud TEI study to the pattern; retire Streamlit app

studies/202512_GenesysCX -> studies/202512_TEI_Genesys_CX_Cloud,
rebuilt as pattern Variant 4 (TEI composite reproduction):

- teicalc/ self-contained engine: Forrester's tables as the never-edited
  verbatim anchor (incl. the p.14 typo note and the $0 AI-token line),
  generic model/scenarios/staging carried over from the Amazon Connect
  study, ClientDrivers overlay (agents / weekly interactions / revenue,
  flat composite so no growth re-base) with ai_tokens_annual as a direct
  input for the token line the published study models at $0
- one deliverable notebook (business_case.ipynb): widget-pair sidebar
  drivers incl. the AI-token price, published-vs-overlay KPI columns,
  cash-flow/waterfall/scenario charts, verification gate, backstage JSON
  data appendix
- gate + tests reproduce the published totals within $2: NPV $10.8M /
  ROI 266% (engine $10,783,466 / 265.79%; payback 3.3 months, not
  headlined in the PDF); 29 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,
  PALLADIUM_GENESYSCX_* keys, ATHENA_EXPECTED reconciliation) deleted;
  git history preserves it

With the last legacy study migrated, the retirement lands too:
- app/ (Streamlit UI) and core/notebook_helpers deleted; nothing else
  imported them
- streamlit stripped from pyproject extras, requirements.txt, Makefile;
  .env.example reduced to the Athena keys; 00_setup.ipynb and
  core/bootstrap.py repointed at the pattern studies
- root README reworked: self-contained studies + slim core/ Athena
  toolkit (tei_client, calculations, export, cli)

All suites green: Genesys 29, Amazon Connect 27, CTM 55, template 7,
root 58.

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

core/bootstrap.py

@@ -7,10 +7,11 @@ From *any* notebook in the repo (root, ``studies/<slug>/notebooks/``, …)::
     pal = init()                       # loads .env, builds client, tests it
     pal.client.list_reports()
 
-or, for a study notebook::
-
-    pal = init(study="202602_AmazonConnect")
-    pal.config.STUDY_SLUG, pal.seed_data.BENEFITS
+(Pattern studies under ``studies/`` are self-contained — they carry their
+own engine and venv and never import ``core``. The legacy ``study=``
+parameter loaded a study's ``config.py``/``seed_data.py``; those modules
+were retired with the study migrations, so ``init()`` is now purely the
+Athena connection bootstrap.)
 
 If ``core`` itself can't be imported (fresh kernel, notebook cwd deep in the
 tree), put this two-liner first — it is the only path juggling left anywhere::