refactor(aidd-context): 00-onboard resolves its providers at runtime

Start with docs/ARCHITECTURE.md and the five reference locations listed in the issue, then inspect the runtime description-matching mechanism used by other recipe skills. Trace the exemption constant and comment in scripts/lib/architecture-rules.js and the guard's tree check. Done means menus resolve and render runnable addresses, missing providers degrade usefully, and the exemption is removed without guard findings.

docs/ARCHITECTURE.md says a recipe skill never hardcodes a sibling provider: it discovers cross-plugin capabilities at runtime through description matching. aidd-context:00-onboard does the opposite — its reference menus name seven sibling addresses outright.

plugins/aidd-context/skills/00-onboard/references/flow.md:27
plugins/aidd-context/skills/00-onboard/references/order/idle-menu.md:7   (two on one line)
plugins/aidd-context/skills/00-onboard/references/state/zones.md:39,40,41
plugins/aidd-context/skills/00-onboard/references/run/tiers.md:12

They are there for a reason: those addresses are what the skill hands a person to type. Replacing them with concept names does not read worse, it stops the menu working. So the fix is not a reword — it is making 00-onboard resolve each menu entry at runtime, by description matching, and render the address it resolved.

Why now

#250 shipped a PreToolUse guard that refuses an edit leaving a plugin's dispatch surface naming a sibling. 00-onboard is exempt from it by a named constant in scripts/lib/architecture-rules.js, carrying a comment that points here. That exemption is the only hole in rule one, and it should close when this lands.

Done when

• 00-onboard names no sibling plugin address in any of its own files.
• Its menus still show the user a runnable command, resolved at run time.
• A menu entry whose provider is not installed degrades to something useful rather than a dead address.
• The exemption constant and its comment are gone from scripts/lib/architecture-rules.js, and the guard is still silent on the tree.