feat(tg): write TG_METADATA_DB_USER/PASSWORD into the compose file

[rboni-dk]

Summary

• Fresh tg install --docker now writes TG_METADATA_DB_USER/PASSWORD into the generated compose file, as a copy of the bootstrap TESTGEN_USERNAME/PASSWORD account — no new Postgres role is created.
• tg upgrade backfills these vars into existing compose files, since TestGen's app-side settings are dropping the silent fallback from TG_METADATA_DB_USER/PASSWORD to TESTGEN_USERNAME/PASSWORD (hard cutover, no default).
• The upgrade backfill validates the bootstrap credentials are actually present/extractable before writing anything (aborts with a clear message otherwise), and only inserts whichever half (user/password) is actually missing, so a partially-migrated or hand-edited file doesn't get corrupted or duplicated.

Release-order dependency

This needs to ship (and reach users) before the TestGen app image that requires TG_METADATA_DB_USER/PASSWORD with no fallback gets published — otherwise existing Docker installs that pull that image via tg upgrade's --policy always lose their metadata-DB credentials entirely. Coordinating with the TestGen app team, who are holding their release until this is confirmed merged.

Test plan

• ruff check / ruff format --check clean
• Full pytest suite green (269 passed), including 2 new regression tests for the upgrade-backfill edge cases (partial-key repair, abort on missing bootstrap creds)
• Manually verified against real Docker/Postgres (not mocks): fresh-install compose passes docker compose config and its TG_METADATA_DB_USER/PASSWORD authenticate via psql; upgrade backfill on a legacy file recovers the account already initialized in an existing Postgres volume; abort path leaves a corrupted file untouched

🤖 Generated with Claude Code

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
dk-installer.py	1948	379	81%	159–160, 164–165, 177–189, 217–218, 221, 226–230, 240–241, 250–262, 267, 280, 326–327, 391, 431–438, 445, 457, 479–480, 529, 579–582, 601–602, 604, 654–683, 687–724, 755–773, 844, 915–916, 984, 1001–1002, 1019–1024, 1098–1099, 1109, 1125–1129, 1132, 1135, 1138, 1149–1182, 1291, 1297, 1343, 1346, 1353–1354, 1360–1362, 1522–1537, 1540–1551, 1568–1569, 1606–1607, 1633–1634, 1641, 1646, 1652–1653, 1686–1689, 1698–1699, 1704–1705, 1778–1780, 2070–2073, 2185–2188, 2225, 2274, 2299–2301, 2316–2318, 2485–2486, 2504, 2534, 2543, 2546–2548, 2591–2603, 2608–2615, 2623–2633, 2782–2795, 2829–2830, 2870–2871, 2885, 2944, 2963–2964, 3216–3218, 3221–3223, 3294, 3359, 3364, 3416–3418, 3421–3423, 3449–3452, 3490–3492, 3495–3497, 3524–3529, 3635–3637, 3645–3649, 3713–3715, 3722–3724, 3735–3738, 3743–3744, 3750–3751, 3762–3771, 3780–3834, 3878–3893
TOTAL	1948	379	81%

Tests	Skipped	Failures	Errors	Time
269	0 💤	0 ❌	0 🔥	3.096s ⏱️