Fix #109: connect --language and --country to export request options

[jacalata]

Closes #109.

Motivation

--language was threading through to request_options.language on
export, but --country never reached the REST API. Classic combined
the two into a BCP 47 locale (en-GB, de-DE, pt-BR) so exports
formatted numbers, dates, and currency for that region. tabcmd 2's
--country was cosmetic.

Behavior change

For users:

• _resolve_locale() joins --language + --country into a
  lang-COUNTRY locale string when both are set; falls back to
  language alone if only that is supplied.
• --country alone now logs a WARNING that names the ignored country
  code and drops it (matching Classic which required --language with
  --country). Previously silently dropped.
• --country choices relaxed from the incorrectly-populated language
  codes (de|en|es|...) to any 2-letter code (upper-cased), so users
  can actually pass GB, MX, BR, etc.
• Locale threads through apply_png_options / apply_pdf_options /
  apply_csv_options.

Test plan

• tests/commands/test_datasources_and_workbooks_command.py — 8
  new tests cover combined locale for PNG/PDF/CSV, country-only drops
  with a warning, language-only pass-through does not warn
• Full test suite passes

🤖 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	169	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	222	31	31	86%
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	2885	458	84%