fix: scaffold submodules input in consumer ci.yml (#39)

[kazmosahebi]

Refs #39. Scaffold half of the submodules story (PR #40 added the workflow input).

Problem

hyperi-ci init -> _render_workflow() only emits tag / from-head / bump (plus optional publish-target) into the generated consumer ci.yml. So the submodules input from #40 never reaches a consumer through the scaffold, and a hand-added submodules: line is clobbered on the next init --force.

Change

• init reads a submodules: field from .hyperi-ci.yaml (_detect_submodules, mirroring detect_license).
• _render_workflow emits submodules: <value> into the with: block when set (mirrors the existing publish-target conditional).
• _render_hyperi_ci_yaml round-trips the field, so re-init preserves it.
• Runtime-safe: CIConfig is .get()-based with no strict validation, so the new key is ignored by the config loader -- it's init-only.
• docs/LESSONS.md: the public-submodule path now points at the .hyperi-ci.yaml field + init render.

Result

.hyperi-ci.yaml:

submodules: schemas

hyperi-ci init renders ci.yml:

    with:
      tag: ${{ inputs.tag || '' }}
      from-head: ${{ inputs.from-head || '' }}
      bump: ${{ inputs.bump || 'auto' }}
      submodules: schemas
    secrets: inherit

Verification

• tests/unit/test_init.py: 51 passed.
• Field declared in .hyperi-ci.yaml is ignored by the runtime config loader (confirmed CIConfig reads only known keys).

Together with #40, a consumer with a public submodule sets one field in .hyperi-ci.yaml and re-runs hyperi-ci init -- no manual workflow editing.