fix(ansible): replace deprecated entities and sync version requirements (#478)

* refactor(ansible): replace deprecated with_items and ansible facts

Replace deprecated `with_items` with `loop` keyword across all roles.
Migrate from legacy `ansible_*` top-level facts to `ansible_facts['*']`
syntax to prepare for ansible-core 2.24 where INJECT_FACTS_AS_VARS
will default to False.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Aleksei Sviridkin <f@lex.la>

* chore(ansible): sync minimum version requirements to 2.15

Align version checks in prereq and airgap roles with README requirement
of ansible-core 2.15+.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Aleksei Sviridkin <f@lex.la>

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Signed-off-by: Aleksei Sviridkin <f@lex.la>
Co-authored-by: Claude <noreply@anthropic.com>