feat(commands): support online template rendering in apply command

[lexfrei]

When talm apply -f nodes/node0.yaml uses the template rendering path (modeline contains templates), it currently runs with Offline: true because the Talos client is not available at rendering time.

This means Helm templates that use lookup() will not work in the apply command. Users must use the two-step workaround:

talm template -f nodes/node0.yaml | talm apply --insecure -f -

To support online rendering, the apply command would need to establish the Talos client connection before template rendering, which requires restructuring the current flow where the client is created after config generation.

Introduced in PR #113.

[lexfrei]

Resolved by #119 (merged in a3d5771), which moved template rendering in talm apply into the Talos client callback so lookup() calls now resolve against live discovery data. The two-step talm template ... | talm apply -f - workaround is no longer required.

Follow-up cleanups split out into #120, #121, #122, #123.

Closing.