fix(volumes_from): keep the ro/rw access mode of a service reference

[breken-ai]

What I did

volumes_from entries that point at a service lost their access mode. resolveVolumeFrom (pkg/compose/service_containers.go) swaps the service name for the id of the service's container. It split the entry on : and kept only the name, so this:

services:
  data:
    image: redis:7-alpine
    command: ["sleep", "3600"]
    volumes: [shared:/shared]
  reader:
    image: redis:7-alpine
    command: ["sleep", "3600"]
    volumes_from:
      - data:ro
volumes:
  shared:

reached the engine as VolumesFrom: ["<id>"], and reader could write to data's volumes. The container:<name>:ro form lost its mode the same way (only spec[1] was kept).

The fix keeps the :ro / :rw suffix when it resolves both forms.

Behaviour with docker compose up -d, then docker inspect reader and touch /shared/x inside reader (engine 27.5.1):

build	HostConfig.VolumesFrom	/shared RW	touch /shared/x
main @ 32bddfc	["cf1d…f683"]	true	succeeds
this branch	["e4b9…f0e9:ro"]	false	Read-only file system

Tests:

• New TestResolveVolumeFromKeepsAccessMode covers db:ro, container:external:ro, db:rw, db and container:other. It fails on main ("db-ctr-id" vs "db-ctr-id:ro", and "external" vs "external:ro") and passes here.
• go test ./pkg/... ./cmd/... passes, except 3 pkg/watch tests (TestGitBranchSwitch, TestWatchBrokenLink, TestWatchCountInnerFile) that fail the same way on main on macOS.
• golangci-lint run --build-tags e2e ./pkg/compose/... (v2.13.2, the version pinned in the Dockerfile): 0 issues.

Note: services that declare :ro/:rw get a different resolved config hash, so the next up recreates them once. That is how their mounts get the mode they asked for.

This PR includes AI_AGENT_DISCLOSURE.md as AGENTS.md asks. The ai-disclosure gate blocks merge until a human reviews the change and removes the file.

Related issue

No open issue found. #1750 and #1188 asked for :ro support in volumes_from, which compose v1 had.

(not mandatory) A picture of a cute animal, if possible in relation to what you did

🐢 (a turtle's shell is read-only too)

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