Reorganize devcontainer compose into colocated per-stack folders

[justinmerrell]

What & why

The devcontainer's local services and tooling were split across two parallel trees — Compose fragments in .devcontainer/compose/ and their config files in .devcontainer/config/ — so understanding one stack meant jumping between folders, and compose/ named the file type rather than what a developer is looking for.

This restructures everything into a single stacks/ folder where each service owns its whole footprint (its compose.yaml plus any config), colocated in one place:

.devcontainer/
  compose.yaml                    orchestrator (include list + network) — unchanged location
  stacks/
    postgres/{compose.yaml, init/}
    redis/compose.yaml
    minio/compose.yaml
    registry/compose.yaml
    azimutt/compose.yaml
    observability/{compose.yaml, config/}
  config/shell/                   left in place (not a stack)

Why this shape (over a services/ vs tooling/ split): colocation makes each stack self-describing and independently runnable; a hard category split adds a fuzzy "which bucket?" tax on every addition, and the optional-vs-default signal it would carry is already expressed by Compose profiles (postgres is always-on; the rest are profile-gated). Naming every fragment compose.yaml is also a standard name that improves Dependabot image detection (the old non-standard names were flagged as friction in dependabot.yml).

Changes

• Moved all 6 fragments → stacks/<name>/compose.yaml; config/postgres/* → stacks/postgres/init/; config/observability/* → stacks/observability/config/ (all tracked by git as renames, content preserved).
• Rewrote bind mounts to stack-relative paths (./init, ./config/...).
• Updated references: compose.yaml include list, validate.yaml CI grep path, dependabot.yml scan dirs (/.devcontainer/stacks/**), and CONFIGURATION.md.
• Unchanged (target the root compose.yaml, which didn't move): devcontainer.json, startup.sh, the dc alias, .env auto-discovery. config/shell/ stays put — it's devcontainer shell setup, not a stack.

Verification

• docker compose -f .devcontainer/compose.yaml --profile observability config resolves all includes; every bind-mount source now resolves into stacks/… (confirmed none point at the old paths).
• Runtime: recreated postgres and confirmed it serves init SQL from the new ./init mount; DB healthy, data preserved.
• CI floating-tag grep with the new stacks/ path still reaches all 6 fragments and passes.

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