feat(generate): port local-stack stack generation to Deno

[wax911]

Closes #4

• Full port of tools/generate_stacks.py (432 lines) to Deno
• Compose file discovery with x-stack metadata grouping
• Fragment merge (docker-compose + swarm.fragment)
• Path rewriting, volume collection, Compose-key stripping
• Deterministic YAML output with sorted keys
• 60 tests for discover, load, merge, transform, volumes, generate

[wax911]

Review notes against #4:

1. Path rewriting is incorrect for multi-service stacks. generateSingleStack() rewrites every service using sources[0]?.composeDir. In local-stack, each service lives in its own directory, so env-file and bind-mount paths for every service after the first can be rewritten relative to the wrong directory.

2. The network name is hardcoded as traefik-public. The issue requires the generated network block to come from config. traefik-public is the local-stack default, not a universal stackctl assumption.

3. Top-level volume metadata is lost. The local-stack Python generator preserves volume metadata such as explicit name: overrides when emitting external volumes. This implementation emits only { external: true } for collected names.

4. The command currently discovers all stacks when options.stacks is omitted, but it does not appear to honor configured stack names/order from .stackctl. Determinism should come from config first, discovery second.

5. The generated YAML contains a generated header comment. That is fine for output readability, but ensure snapshot tests account for it and that sync comparisons do not drift against existing local-stack generated output unless the migration intentionally updates those files.

This is close in shape, but the path-rewrite bug is a correctness blocker for the actual local-stack repository.

[wax911]

Follow-up review after the push:

Good fixes:

• The multi-service path rewrite issue is addressed with a service-to-compose-directory map.
• The network name is now configurable through GenerateOptions.network instead of being only hardcoded.
• Existing top-level volume definitions are preserved and get external: true when missing.
• Config stack names are now accepted through configStackNames.

Remaining issues:

1. The PR is currently not mergeable and its base SHA is behind the current config PR. Rebase it after #18 is fixed.

2. The default network still falls back to traefik-public. That is fine as a local-stack default, but it should come from DEFAULT_CONFIG/config wiring rather than being a universal compose module default. If this is intentionally the built-in default, document it as such.

3. Confirm snapshot compatibility against current local-stack generated stacks. The added generated header comment and key sorting may intentionally change output, but sync must not produce noisy drift during migration unless local-stack updates the committed stack artifacts in the same migration.

4. Make sure the service-dir map handles duplicate service names across different compose sources deterministically. The first entry wins today; that should either be validated as an error or documented.

This is much closer. The previous correctness blocker is fixed, but mergeability and parity validation still need attention.