Implement BitLogin as a modular protocol library, embeddable widget, and demo site

Builds out the v0.3 spec as an npm workspace monorepo any static site can
consume for login and Nostr signing:

- packages/core: framework-free protocol implementation — Argon2id/HKDF/
  ScalarExpand/AES-256-GCM/JCS crypto primitives, NIP-01 event handling and a
  quorum-aware relay pool, credential/recovery capsule construction and
  validation, and the full account lifecycle (registration, any-device
  login with rollback/relay-disagreement detection, phrase recovery with
  recovery-capsule refresh, password rotation with mandatory tombstone +
  NIP-09 deletion, replica repair, recovery export, NIP-19 encoding, a
  NIP-44 v2 implementation, and a NIP-07-shaped signer). 49 tests cover the
  spec's Phase 0 byte-level vectors plus full create/login/recover/rotate
  end-to-end scenarios against an in-memory mock relay.

- packages/widget: a <bitlogin-auth> custom element with a dedicated crypto
  Web Worker (private keys never touch the main thread) and a window.nostr
  NIP-07-compatible provider, so existing Nostr web apps work against it
  with zero code changes. Built with Vite into two relocatable static files.

- packages/demo: a plain static site (no build step of its own) consuming
  the widget — a branding/landing page, an integration guide, and an
  account-manager page covering create/login/recover, password rotation,
  and identity export.

All flows were verified twice: protocol-level tests against a mock relay,
and the actual built widget driven end-to-end in real Chromium (registration,
phrase confirmation, event signing, clean-device login, window.nostr, and
phrase recovery all reproduce the identical everyday pubkey).

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01GWJbXXhvTx9wo59jSz57J6

.gitignore

@@ -0,0 +1,6 @@
+node_modules/
+dist/
+dist-types/
+*.tsbuildinfo
+*.log
+.DS_Store