fix: accept yes/no on --encrypt for Classic parity

[jacalata]

Motivation

tabcmd Classic's --encrypt on createextracts takes an explicit
yes or no value. tabcmd 2 treated it as a bare boolean flag,
silently ignoring any following value. Scripts passing --encrypt no
on Classic didn't fail on tabcmd 2 but produced the wrong behavior
(they either bailed on argparse or silently kept encryption on).

Behavior change

For users: --encrypt accepts an optional yes|no|true|false
argument (case-insensitive).

• Bare --encrypt still means True (tabcmd 2 syntax).
• Omitted means False.
• Explicit --encrypt no (or false/0) now means False.

Preserves tabcmd 2's current default while accepting Classic's
yes/no syntax.

Test plan

• tests/parsers/test_parser_create_extracts.py — 8 new tests:
  omitted / bare / yes / no / true / false / case-insensitive /
  bad-value-rejected
• Full test_parser_create_extracts.py suite: 15 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	222	31	31	86%
tabcmd/execution
_version.py	2	2	2	0%
global_options.py	133	8	8	94%
localize.py	66	11	11	83%
logger_config.py	60	6	6	90%
tabcmd_controller.py	42	7	7	83%
TOTAL	2881	458	84%