Add SVG assets for login devices and passkey icons

- Created a new SVG file for login devices with detailed paths and styles.
- Added a new SVG file for the passkey icon with multiple vector paths and fill attributes.

backend/migrations/012_passkeys.sql

@@ -0,0 +1,31 @@
+-- Discoverable WebAuthn credentials used for passwordless sign-in.
+CREATE TABLE passkey_credentials (
+    id SERIAL PRIMARY KEY,
+    user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    credential_id VARCHAR(512) UNIQUE NOT NULL,
+    public_key BYTEA NOT NULL,
+    counter BIGINT NOT NULL DEFAULT 0,
+    transports TEXT[] NOT NULL DEFAULT '{}',
+    device_type VARCHAR(32) NOT NULL,
+    backed_up BOOLEAN NOT NULL DEFAULT false,
+    label VARCHAR(100),
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    last_used_at TIMESTAMP
+);
+
+CREATE INDEX idx_passkey_credentials_user_id ON passkey_credentials(user_id);
+
+-- Challenges are short-lived and single-use. Keeping them in PostgreSQL lets
+-- verification work across backend restarts and multiple application instances.
+CREATE TABLE passkey_challenges (
+    id SERIAL PRIMARY KEY,
+    user_id INTEGER REFERENCES users(id) ON DELETE CASCADE,
+    purpose VARCHAR(32) NOT NULL CHECK (purpose IN ('registration', 'authentication')),
+    challenge VARCHAR(512) NOT NULL,
+    expires_at TIMESTAMP NOT NULL,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    UNIQUE(purpose, challenge)
+);
+
+CREATE INDEX idx_passkey_challenges_lookup
+    ON passkey_challenges(purpose, challenge, expires_at);