refactor(build): replace staging/cp env hack with vite --mode per-environment

- Rename .env.staging → .env.dev (and .default template)
- Add .env.test.default for the test tier (test-api.oneskyit.com)
- build:staging → build:dev/test/prod using vite --mode <name>
- deploy:staging → deploy:dev; add deploy:test
- Dockerfile: ARG BUILD_MODE=dev; explicit .env.runtime copy per mode
- .dockerignore: rewritten (deduped); allow .env.dev/.env.test/.env.prod
- .gitignore: track .env.dev.default and .env.test.default
- Remove dead PUBLIC_AE_* imports from ae_stores.ts (ACCOUNT_ID, EVENT_ID,
  NO_ACCOUNT_ID_TOKEN, SPONSORSHIP_CFG_ID); sponsorship_cfg_id defaults to null
- Strip dead vars from .env.prod.default template (AE_CFG_ID, AE_APP_NODE_PORT,
  ACCOUNT_ID, EVENT_ID, SPONSORSHIP_CFG_ID, NO_ACCOUNT_ID_TOKEN)
- GUIDE__Development.md: build:staging → build:dev

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.prod.default

@@ -1,28 +1,14 @@
-# One Sky IT's Aether Framework and System — PRODUCTION template
+# One Sky IT's Aether Framework and System — PROD template (api.oneskyit.com)
 # Copy to .env.prod and fill in real values.
-# AE_CFG_ID: 1=Default, 5=Home Dev, 7=Live Testing/Prod
-
-# Shared config record (controls SMTP, API routing, external keys from DB)
-AE_CFG_ID=7
 
 # Aether API access
 PUBLIC_AE_API_PROTOCOL=https
 PUBLIC_AE_API_SERVER=api.oneskyit.com
 PUBLIC_AE_API_BAK_SERVER=bak-api.oneskyit.com
 PUBLIC_AE_API_PORT=443
-PUBLIC_AE_API_PATH=
 PUBLIC_AE_API_SECRET_KEY=XXXX
 PUBLIC_AE_API_CRUD_SUPER_KEY=XXXX
 # Bootstrap key: used only for the unauthenticated site-domain lookup on first load.
 # Separate from the main API key — has limited permissions (no account_id required).
 PUBLIC_AE_BOOTSTRAP_KEY=XXXX
 PUBLIC_AE_NO_ACCOUNT_ID=No_Account_ID_Here
-PUBLIC_AE_NO_ACCOUNT_ID_TOKEN=Nothing_to_see_here
-
-# SvelteKit app config
-AE_APP_NODE_PORT=3001
-
-# Default demo/client context (set to the target account for this deployment)
-PUBLIC_AE_ACCOUNT_ID=XXXX
-PUBLIC_AE_EVENT_ID=XXXX
-PUBLIC_AE_SPONSORSHIP_CFG_ID=XXXX