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.dev.default

@@ -0,0 +1,17 @@
+# One Sky IT's Aether Framework and System — DEV template (dev-*.oneskyit.com)
+# Copy to .env.dev and fill in real values.
+
+
+# Aether API access
+PUBLIC_AE_API_PROTOCOL=https
+PUBLIC_AE_API_SERVER=dev-api.oneskyit.com
+PUBLIC_AE_API_BAK_SERVER=test-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
+