feat(learning): the 8 base validators for the roadmap engine

[OthmaneZ05]

Summary of Changes

Implements the 7 remaining validator types for the learning/roadmap validation engine — table_exists, redis_key_exists, mongo_collection_exists, edge_exists, lb_upstreams, port_denied, asg_replicas — alongside the existing container_running. Roadmap steps can now check real Postgres/Redis/Mongo state, network connectivity, and ASG replica counts, not just container liveness.

Design choices, in short:

• DB validators (table_exists, redis_key_exists, mongo_collection_exists) go through containerProvider's executePsqlCommand/executeRedisCommand/executeMongoCommand, using the same query idiom already used by the Postgres/Redis/Mongo explorers.
• edge_exists/port_denied reuse NetworkService's security-group rule expansion (computeSemanticRules, now exposed publicly) instead of re-deriving connectivity from raw security groups — this is the same logic that drives real iptables enforcement, so a validator's verdict always matches what's actually applied.
• asg_replicas/lb_upstreams read directly off ContainerInfo.asgId/isAsgInstance, no new dependency needed.
• A shared resolveRunningContainer/resolveSourceAndTarget helper keeps node targeting, type checks, and pedagogical fail messages (observed vs. expected, plain language, no raw Docker ids) consistent across all 7 validators.
• Docker-not-ready responses from Postgres/Redis/Mongo are treated as a pedagogical fail ("still starting up, try again"), not an infrastructure error — only a genuinely unreachable Docker daemon propagates as error.

Types of Changes

• New feature / node type addition
• Bug fix (non-breaking change resolving an issue)
• Refactoring / structural cleanup
• Documentation update

Verification & Testing

Automated Checks

• Run npm run lint successfully with no errors
• Run npm run build successfully with no compilation errors
• Run npm test successfully (all tests pass — 206 tests, 25 suites)

Manual Verification

Ran the backend against real Docker and exercised container_running, table_exists, edge_exists and port_denied in both pass and fail against real containers, using the existing example roadmap (roadmaps/example-first-architecture.json), which already targets 4 of these 8 types:

• Created/started a real ubuntu node → container_running flips fail → pass.
• Created a real Postgres node, ran CREATE TABLE users (...) through it → table_exists flips fail → pass, including the "database still starting up" pedagogical message before Postgres was ready.
• Applied a real network config with a security-group rule → edge_exists flips fail → pass; widened the rule to all ports → port_denied flips pass → fail, matching the real enforcement policy.
• Cleaned up the demo project/containers afterwards.

Checklist

• My code follows the repository's code style and lint standards
• I have updated the documentation or instructions if necessary
• All unit and integration tests are passing