fix(compose): keep the tier 0 memory overlay in the resolved stack

[roshangupta00750]

Fixes #5466

Problem

docker-compose.tier0.yml caps memory for machines below 8GB RAM. The installer's compose-select.sh adds it and logs Including docker-compose.tier0.yml (Tier 0 memory limits). Phases 03 and 11 then replace COMPOSE_FLAGS with scripts/resolve-compose-stack.sh output, which is cached in .compose-flags. The resolver has never applied the overlay, so a tier 0 install runs on the base limits. Every later resolution drops it again: ods enable/disable, the host agent and ods-update.sh.

With the real compose files (base + cpu), the effective limits on main and with this change:

Service	main	this PR (tier 0)
llama-server	6G	4G
dashboard	2G	512M
dashboard-api	2G	512M
open-webui	4G	1G

Change

The resolver adds docker-compose.tier0.yml for tier 0/T0 when the file exists, before the operator's docker-compose.override.yml, so operator overrides still win. Other tiers are unchanged.

Persisting TIER to .env, so that later resolutions receive tier 0, is the separate change in #6617 and is not duplicated here.

Tests

tests/test-tier0-memory-overlay.sh (registered in tests/ci-suite.txt) runs the real resolver against a minimal tree. It checks:

• tier 0 and T0 include the overlay;
• tier 1 does not;
• the overlay comes before docker-compose.override.yml;
• a tree without the overlay file still resolves.

	macOS (/bin/bash 3.2)	Linux, Ubuntu 26.04
main	—	3 of 5 fail
this PR	5/5	5/5

• Mutation: dropping the T0 spelling fails its check.
• docker compose config on the real base + cpu files: with this change, tier 0 gives the limits in the table above.
• Related suites: test-compose-failure-report.sh and test-compose-image-discovery.sh still pass.
• Checks: list-unwired-tests.py --check passes.

This re-lands the resolver part of #5467, which was closed with the public-beta branch.

AI assistance was used for analysis and drafting the fix and test. I reproduced the failure and verified the results above myself.

[roshangupta00750]

@Lightheartdevs @gabsprogrammer flagging this one because of its user impact: every tier 0 install (machines under 8GB RAM) currently runs without docker-compose.tier0.yml. The resolver drops it, so services get about 14G of memory limits on a 6G host (llama-server 6G instead of 4G, Open WebUI 4G instead of 1G). This is a 10-line resolver change with a CI-registered test, and docker compose config on the real files confirms the tier 0 limits apply. The TIER-in-.env half stays in #6617.