Renovate detects no dependencies in compose.yml.tftpl

[noahwhite]

Bug Summary

Renovate's docker-compose manager fails to detect any packages in compose.yml.tftpl, reporting "None detected" in the Dependency Dashboard (issue #232). The fileMatch regex is correct but the manager silently fails to extract packages, likely due to the Terraform template syntax ($${...}) in the file confusing the YAML parser.

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✅ Acceptance Criteria

• Renovate Dependency Dashboard shows all 5 tracked images as detected dependencies
• Renovate creates a PR when ghost/traffic-analytics (currently 1.0.12, upstream 1.0.148) or any other tracked image has a newer version available
• PR uses feature/renovate- branch prefix, targets develop, and is assigned to noahwhite

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📝 Additional Context

Root cause: The docker-compose manager uses a YAML parser that chokes on Terraform template syntax in .tftpl files. "None detected" despite correct fileMatch is the symptom.

Fix: Replace the docker-compose manager with a customManagers regex approach that bypasses YAML parsing entirely. The regex matches digest-pinned image lines directly:

image: (?<depName>[^:\s$]+):(?<currentValue>[^@\s]+)@(?<currentDigest>sha256:[a-f0-9]+)

This correctly matches all 5 pinned images and skips ghost:${GHOST_VERSION:-6-alpine} (no digest).

Tracked images:

• caddy
• mysql
• ghost/traffic-analytics
• ghcr.io/tryghost/activitypub
• ghcr.io/tryghost/activitypub-migrations

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✅ Definition of Done

• All acceptance criteria met
• Renovate Dependency Dashboard updated after next run
• No regressions to existing Renovate behavior (GitHub Actions tracking still works)

[linear]

GHO-106