fix(cli): preserve provider instances and child prompt isolation

[Brian Krabach (bkrabach)]

Why

Finalize the reviewed CLI fixes for provider-instance correctness and in-process self-child prompt isolation, with the merged Foundation prompt-factory API pinned explicitly.

Changes

• Preserve configured provider instance IDs and their per-instance configuration during provider inspection.
• Build self-child prompt factories from the root prepared bundle for the target child, render once, and install only the frozen result.
• Keep nested self-child behavior based on the already-rendered child prompt rather than reusing a parent-installed factory.
• Pin amplifier-foundation to merged commit 4f7c482438e05bd678eb92e899ef181a8a0e267e.
• Includes the four current main commits already present before this fix branch was prepared.
• Foundation prerequisite: #380. Provider prerequisite: feat(cli): Execute trailing text after mode slash commands as first prompt #87.

Tests

• Locked dependency sync passed with the merged Foundation revision.
• Focused child-prompt and resume tests: 15 passed.
• No live model/API calls were made.
• Full CI remains the release gate.

Limitations

• This PR does not add WebSocket transport, async tool orchestration, mid-turn steering, Batch transport, or other new feature surfaces.
• No live acceptance claim is made.