Android: build:android establishes its own precondition

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Root build:android ran the port's build without establishing what that build needs, so a fresh
clone produced an APK that crashed on the device instead of failing at build time.

Two separate gaps, both measured:

• @learn6502/core was not built. The port's build needs it; a session had to run
  gjsify workspace @learn6502/core build by hand to get an APK at all. --with-dependencies
  fixes this one, and start:android now builds before it starts.
• @learn6502/learn was never declared a dependency of app-android — even though learn's
  own build copies its generated tutorial.ns.xml and quick-help.ns.xml straight into
  app-android/app/mdx/. That relationship is a FILE COPY across a workspace boundary, not an
  import, so it is invisible to module resolution and to --with-dependencies. The APK built
  successfully with an empty app/mdx/ and only crashed on-device when opening the tutorial.

The second one is the reason this is worth a note in AGENTS.md rather than just a script edit: a
build-graph edge that no import expresses cannot be derived, so it has to be declared.

Found while chasing the hex-monitor fix (#193), where the missing build showed up as a runtime
crash rather than a build failure.

Checked: check-workspace-scripts green, both manifests parse, build byproducts kept out of the
commit.

🤖 Generated with Claude Code