bug: upgrade --migrate-directory exits early, skips the actual upgrade #125

Problem

When a user runs npx github:bradygaster/squad upgrade --migrate-directory, the command:

1. Renames .ai-team/ → .squad/
2. Updates .gitattributes and .gitignore
3. Scrubs email addresses
4. Calls process.exit(0) and stops

The normal upgrade flow (copying squad.agent.md, updating workflows, writing .ai-team-templates/, running version-specific migrations) never runs.

Reproduction

Reproduced against bradygaster/SqncR (squad v0.3.0):

node squad-v050-index.js upgrade --migrate-directory
# Result: .ai-team/ renamed to .squad/, squad.agent.md still at v0.3.0

Expected vs Actual

Root Cause

index.js line 1181: process.exit(0) terminates the process after directory migration, before the upgrade logic executes.

Fix

After the migration block completes successfully, fall through to the normal upgrade flow instead of exiting. The isMigrateDirectory flag should trigger the rename as a pre-step, not as an exclusive path.

Impact

Any user upgrading from .ai-team/-based installs (pre-0.5.0) to 0.5.0+ using the documented --migrate-directory flag ends up with a migrated directory structure but stale Squad files. The help text implies the flag works alongside upgrade, not instead of it.

Found by: Diagnostic run on SqncR — investigation triggered by reported 0.5.0 issues.