Fix #434: map "Local" auth_setting to ServerDefault

[jacalata]

Closes #434.

Motivation

tabcmd Classic accepts Local as an auth type on the CLI and in CSV
column 7, but TSC's UserItem.Auth enum has no Local value, so
passing it through crashed on server.users.add. Anyone importing a
Classic-authored CSV containing Local in column 7 hit a hard failure.

Behavior change

For users: Userdata.to_tsc_user() maps Local (case-insensitive)
to TSC.UserItem.Auth.ServerDefault and logs a WARNING naming the
affected user so the operator sees the remap happened. A silent remap
would be surprising -- if the site's actual default auth isn't the
same as Classic's Local, created users would have a different auth
method than intended.

Test plan

• tests/commands/test_user_utils.py — 3 new tests cover exact-case
  Local, lowercase local, and non-Local pass-through
• Test asserts the WARNING is emitted
• Full test_user_utils.py suite: 18 passed

🤖 Generated with Claude Code

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
tabcmd
__main__.py	12	12	12	0%
_version.py	11	11	11	0%
tabcmd.py	15	15	15	0%
version.py	9	5	5	44%
tabcmd/commands
commands.py	10	10	10	0%
constants.py	77	18	18	77%
server.py	135	18	18	87%
tabcmd/commands/auth
session.py	394	50	50	87%
tabcmd/commands/datasources_and_workbooks
datasources_and_workbooks_command.py	157	18	18	89%
datasources_workbooks_views_url_parser.py	142	5	5	96%
delete_command.py	60	16	16	73%
export_command.py	120	25	25	79%
get_url_command.py	127	47	47	63%
publish_command.py	123	28	28	77%
runschedule_command.py	21	7	7	67%
tabcmd/commands/extracts
create_extracts_command.py	42	8	8	81%
decrypt_extracts_command.py	27	2	2	93%
delete_extracts_command.py	37	6	6	84%
encrypt_extracts_command.py	27	2	2	93%
extracts.py	20	2	2	90%
reencrypt_extracts_command.py	27	2	2	93%
refresh_extracts_command.py	48	10	10	79%
tabcmd/commands/group
create_group_command.py	29	5	5	83%
delete_group_command.py	27	2	2	93%
tabcmd/commands/project
create_project_command.py	46	8	8	83%
delete_project_command.py	35	4	4	89%
publish_samples_command.py	30	4	4	87%
tabcmd/commands/site
create_site_command.py	34	5	5	85%
delete_site_command.py	27	2	2	93%
edit_site_command.py	38	2	2	95%
list_command.py	77	12	12	84%
list_sites_command.py	29	2	2	93%
tabcmd/commands/user
add_users_command.py	29	5	5	83%
create_site_users.py	58	11	11	81%
create_users_command.py	59	9	9	85%
delete_site_users_command.py	43	5	5	88%
user_data.py	226	30	30	87%
tabcmd/execution
_version.py	2	2	2	0%
global_options.py	125	8	8	94%
localize.py	66	11	11	83%
logger_config.py	60	6	6	90%
tabcmd_controller.py	42	7	7	83%
TOTAL	2877	457	84%