feat(cli): rework claim to OTP-only — drop device flow + browser + polling

Replace claim_via_device_flow / claimViaDeviceFlow with claim_via_otp /
claimViaOtp. The new flow:
  1. POST /api/v1/auth/email_code/ with the user's email
  2. Prompt for the verification code (or accept via --code for non-TTY)
  3. POST /.../verify/ with {email, code, agent_mode_api_key: <local key>}
  4. Backend's verify_email_code runs upgrade-in-place inline and returns
     {claimed: true, claimed_at, ...}

No browser open, no localhost:3000 frontend dependency, no 10-minute poll
loop. Just two HTTP calls + an OTP prompt. Same upgrade-in-place
semantics on the backend; same key-value-unchanged guarantee for the
caller.

--code flag still supported on `mem0 init --email` for non-interactive
use (CI, agent-driven claim scripts).

cli/python/src/mem0_cli/commands/init_cmd.py

@@ -203,7 +203,7 @@ def run_init(
         email-based key.
     """
     from mem0_cli.agent_detect import detect_agent_caller
-    from mem0_cli.commands.agent_mode_cmd import bootstrap_via_backend, claim_via_device_flow
+    from mem0_cli.commands.agent_mode_cmd import bootstrap_via_backend, claim_via_otp
     from mem0_cli.state import is_agent_mode as _global_agent_mode
     from mem0_cli.telemetry import capture_event
 
@@ -235,7 +235,7 @@ def run_init(
             email = email.strip().lower()
             _validate_email(email)
             print_info(console, f"Claiming Agent Mode account to {email}...")
-            claim_via_device_flow(existing, email=email)
+            claim_via_otp(existing, email=email, code=code)
             _fire_init("email", claimed=True)
             return