feat: add terraform module to install the lambda scope

[andres-nullplatform]

Adds lambda/specs/install/ — the OpenTofu module that registers the AWS Lambda
scope in nullplatform: service spec, scope type, the 14 action specs, and the
agent notification channel.

Branched fresh from main to replace #40, which carried the install module
alongside unrelated CI changes (removal of the release-please workflow and the
conventional-commit / branch-name checks) that conflicted with the chained
release pipeline merged in #41. This PR is the install module only.

File	Purpose
main.tf	scope_definition + scope_definition_agent_association (tofu-modules v6.19.1)
variables.tf	Inputs; only nrn, np_api_key, tags_selectors are required
provider.tf	nullplatform, http, external, null providers
backend.tf	S3 state at lambda/install/terraform.tfstate
terraform.tfvars.example	Template to copy to the gitignored terraform.tfvars