Isolate charm/log demo into its own example module

[evanmschultz]

Summary

Move the real charm.land/log/v2 transcript demo out of the root module graph and into its own nested example module.

Why

Today the real log transcript generation lives in internal/examples, so charm.land/log/v2 is pulled into the root go.mod even though it is only needed for the focused log demo.

That is valid Go, but it is not the clean dependency posture we want for laslig.

Goal

Keep the user-facing behavior the same while isolating the demo-only dependency:

• keep shared example rendering helpers in internal/examples
• move the actual charm/log usage into its own nested example module
• keep mage demo behavior the same from the user’s point of view
• keep README, focused examples, and VHS assets unchanged from the user’s point of view
• remove charm.land/log/v2 from the root module graph

Likely Shape

• nested example module under something like examples/logblock/ or examples/logging/
• local replace github.com/evanmschultz/laslig => ../..
• update Mage/demo/VHS wiring for that one example path

Acceptance Criteria

• root go.mod no longer requires charm.land/log/v2
• the log-focused demo still shows a real Charm log transcript
• mage demo, mage check, and mage vhs still pass
• README and GIFs stay aligned with the runnable examples