Provision installed custody and chain prerequisites (ELACITY-2297) #44

From the 0.7 completion checklist in #38 (unfinished at merge time).

Provision the installed custody and chain prerequisites for the protected-content path:

• Signed, owner-only 3-node 2-of-3 custody composition.
• Private multi-source Chain config with funded accounts.
• Packaged protect + custody + decrypt providers via installer/ProviderRegistry.
• Done in feat(protected-content): provision installed custody and chain prerequisites #52: protected-content-decrypt-provider is registered and boot runs reconcile_runtime_custody_viewers_after_decrypt_registration.
• Remaining: prove the installed configuration above and the packaged providers on a real install.

Tracked as ELACITY-2297. No dependencies. Blocks #45, #46 and #47. Status lives in this issue.