feat(storage): Blossom Phase 0 — flag + vendored SDK + service skeleton (#30)

Phase 0 of docs/blossom-plan.md. No UX; off-by-default ("off = no trace").

- Vendored: pinned [email protected] bundled by scripts/build-blossom-sdk.mjs
  → vendor/blossom-client-sdk.bundle.min.js (esbuild, browser ESM, ~27KB). The
  optional @cashu/cashu-ts peer dep (BUD-07 payments, only reached on a lazy 402
  branch bitvid never hits) is aliased to a throwing stub. `npm run build:blossom-sdk`.
- Flag: FEATURE_BLOSSOM_STORAGE wired like FEATURE_AUDIO_INGEST / _BITCOIN_CONNECT
  (instance-config → config → constants), default FALSE.
- Service: js/services/blossomService.js implements the same
  uploadFile({…}) → {url,key} contract as s3UploadService (so a later
  isBlossomProvider branch drops into mediaUploader). Lazy-loads the SDK; core
  path = createUploadAuth(signer, sha256) + multiServerUpload (BUD-11 auth via
  bitvid's existing signer, BUD-04 mirror). Torrent parity + result-shape mapping +
  mediaUploader wiring + Storage-pane config land in Phase 1.

Tests: tests/blossom-service.test.mjs (5 — availability gate + input guards).
Lint + build clean. Nothing wired into the app yet.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

package.json

@@ -15,6 +15,7 @@
     "build:beacon:bundle": "node scripts/build-beacon.mjs",
     "build:beacon": "npm run build:beacon:bundle && npm run lint:inline-styles",
     "build:bitcoin-connect": "node scripts/build-bitcoin-connect.mjs",
+    "build:blossom-sdk": "node scripts/build-blossom-sdk.mjs",
     "ci:beacon": "npm run build:beacon",
     "format": "prettier --cache --write css/tailwind.source.css css/tokens.css css/docs.css \"docs/**/*.html\" tailwind.config.cjs README.md CONTRIBUTING.md",
     "audit": "node scripts/daily-design-system-audit.mjs",
@@ -60,6 +61,7 @@
   "devDependencies": {
     "@getalby/bitcoin-connect": "3.12.3",
     "@playwright/test": "^1.58.2",
+    "blossom-client-sdk": "5.0.0",
     "cssnano": "^7.1.2",
     "fake-indexeddb": "^6.2.5",
     "jsdom": "^28.1.0",