Shadow bundle context should guide iterative development workflow

[obra]

Problem

When using shadow environments for iterative development, I ran into a workflow gap that caused confusion and wasted time.

What happened

1. Created a shadow environment with local sources for amplifier-app-cli and amplifier-module-hooks-streaming-ui
2. Tested changes - they worked
3. Made additional commits locally to fix issues found during testing
4. Assumed the shadow would have the new commits
5. Tested again - changes weren't there
6. Spent time debugging why the "fix" wasn't working, when the real issue was the shadow had a point-in-time snapshot

Root cause

The shadow instructions (amplifier-bundle-shadow/context/shadow-instructions.md) mention that snapshots are point-in-time, but don't provide clear workflow guidance for the common iterative development pattern:

write code → create shadow → test → find issue → fix locally → test again → ???

The missing step is: use add-source to sync new commits into the running shadow.

Proposed change

Add a section to context/shadow-instructions.md in the shadow bundle:

## Iterating on Local Changes

Shadow environments snapshot your local repos **at creation time**. When you make new commits locally after creating a shadow, those changes are NOT automatically available.

**To sync new local commits into a running shadow:**

1. Use `add-source` to push the new commit:
   ```bash
   shadow add-source <shadow-id> /path/to/local/repo:org/repo-name

2. Clear any module/package caches inside the shadow that may have the old version

3. Re-test

Alternative: Destroy and recreate the shadow to get a fresh snapshot with all current commits.

Common mistake: Assuming new local commits are automatically available in existing shadows. They are not - shadows are isolated snapshots.

This would help AI agents (and humans) understand the correct workflow for iterative development with shadow environments.

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*Note: Filed here because `microsoft/amplifier-bundle-shadow` has issues disabled.*