fix(compose): layer tier0 memory overlay in compose resolver

[vaibhavsrv]

Fixes #5466

Why this matters

docker-compose.tier0.yml defines capped memory limits for low-RAM machines (<8GB RAM): capping llama-server at 4G (instead of 6G), dashboard containers at 512M (instead of 2G), and Open WebUI at 1G (instead of 4G). While installers/lib/compose-select.sh logs that it includes this overlay when TIER=0, subsequent phases and the CLI re-resolve the stack via scripts/resolve-compose-stack.sh, which previously lacked handling for docker-compose.tier0.yml. As a result, the overlay was discarded, and low-RAM machines ran with higher baseline limits that exceeded available host memory.

This change teaches resolve-compose-stack.sh to layer docker-compose.tier0.yml whenever tier is resolved as 0 or T0 (matching installer convention) and the file is present in the compose directory. Higher tiers and non-Tier 0 configurations remain untouched.

Validation

• Baseline reproduction: Running resolve-compose-stack.sh --tier 0 --gpu-backend cpu omitted docker-compose.tier0.yml, outputting only base and cpu compose files.
• Post-fix verification: Running ods/tests/test_resolve_compose_tier0_overlay.py confirms that --tier 0 and --tier T0 include -f docker-compose.tier0.yml, whereas --tier 1 cleanly excludes it.
• Telemetry: Compose resolver test suite passes: test_resolve_compose_tier0_overlay.py passes cleanly (exit code 0). Wired into Linux CI workflow under compose resolution tests.

Overlap check

• Issue Tier 0 installs never get the tier 0 memory overlay: the compose resolver drops docker-compose.tier0.yml #5466: Directly resolves the open defect reported by @roshangupta00750 regarding Tier 0 installs missing the tier0 memory limits overlay.
• fix(compose): guard non-mapping service field in extension manifests #5953: Addressed manifest service mapping validation in extension discovery loops. This PR focuses strictly on the root compose overlay resolution for low-memory tiers.
• Does not modify multi-GPU overlays, macOS cloud auth overrides, or extension discovery logic.

Risk / AI disclosure

AI-assisted investigation, implementation, and test regressions. This aligns resolve-compose-stack.sh with existing installer expectations in compose-select.sh. Independent human review and platform/runtime qualification remain gates. No running configuration, deployment or upstream merge changed.

Follow-up integration evidence

Composed with #5871, #5951, #5952, #5953, and #6076 at HEAD without conflicts. Production and test diffs passed together; resolver and compose contracts remain intact.
Backlog composition was local-only (production/test diffs, excluding workflow/Makefile wiring); it is not an upstream merge or independent human approval. Declared live-review gates remain open.

[Lightheartdevs]

Thanks for this contribution. public-beta was promoted into main on 2026-09-24 and no longer receives changes, so we're closing pull requests that target it. This isn't a judgment on the change itself. If it's still needed, please rebase onto main and open a focused PR. See #7253 for details and the contribution policy.