Sync 2: device-token bearer auth + linked-devices UI (M8)

Native clients (Tauri/Android) authenticate sync with a long-lived device
bearer token, alongside the existing web session cookie.

Backend:
- security.py: generate_token() (secrets.token_urlsafe) + hash_token()
  (SHA-256 — device tokens are already high-entropy, so no slow KDF; keeps
  per-request bearer auth cheap). Only the hash is stored.
- device_tokens table (migration 0016): id, user_id, token_hash (unique),
  name, created_at, last_used_at.
- login_required now accepts `Authorization: Bearer <token>` OR the session
  cookie. Session path stays DB-free (fast); bearer path looks up the token
  hash, sets g.user_id, and stamps last_used_at.
- Endpoints: POST /api/auth/device-login (public; email+password → token,
  the native first-link flow), POST /api/auth/devices (session/bearer →
  token, web "link a device"), GET /api/auth/devices (list), DELETE
  /api/auth/devices/<id> (revoke). All owner-scoped; token shown once.

Frontend:
- Per-user (not admin) /account view "Linked devices": create a token
  (one-time reveal + copy), list devices (name, linked/last-synced), revoke
  with confirm. Top-bar device icon for all users; devices Pinia store.

Tests (DB-free): token hash determinism + uniqueness; device endpoints
auth-guard (401 without auth, before DB); device-login input validation.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

alembic/versions/0016_device_tokens.py

@@ -0,0 +1,36 @@
+"""device_tokens (M8 sync hub, step 2)
+
+Revision ID: 0016
+Revises: 0015
+Create Date: 2026-07-23
+
+Long-lived bearer tokens for native clients (Tauri/Android) to authenticate sync.
+Only the SHA-256 hash of each token is stored; the plaintext is shown once at
+creation. Owner-scoped + individually revocable.
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID
+
+revision = "0016"
+down_revision = "0015"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "device_tokens",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True),
+        sa.Column("user_id", UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("token_hash", sa.Text(), nullable=False, unique=True),
+        sa.Column("name", sa.Text(), nullable=False, server_default=""),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.Column("last_used_at", sa.DateTime(timezone=True), nullable=True),
+    )
+    op.create_index("ix_device_tokens_user", "device_tokens", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_device_tokens_user", table_name="device_tokens")
+    op.drop_table("device_tokens")