fix: migrate sessions from global to git project after init

[Wangmerlyn]

Fixes#16812

Problem

Sessions created before a git repository has commits are stored under project_id = "global". When a commit is made and opencode resolves a real project ID (the root commit SHA), the sessions were not being migrated properly.

Root Causes

1. FK constraint violation:migrateFromGlobal() was called before the target project row was inserted into the project table, causing the UPDATE to be rejected due to the foreign key constraint on session.project_id.
2. One-shot gate: The migration only ran inside the if (!row) branch — i.e., only when a new project row was created. Sessions accumulated under "global" after the real project row already existed were never migrated.

Solution

• Moved migrateFromGlobal() call to after the project row is inserted/updated
• The migration now runs every time fromDirectory is called with a non-global project ID, not just when creating a new project row
• Added a test case that reproduces the bug scenario

Verification

• New test passes: migrates sessions from global to git project after git init
• All existing project tests pass (18 tests)
• Typecheck passes for all packages

[github-actions]

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Found a potential related PR:

PR #16814: fix(opencode): sessions lost after git init in existing project
#16814

This PR appears to address the same issue as PR #17150 - sessions being lost or not properly migrated when git is initialized in an existing project. Both PRs deal with the project_id = "global" problem and session migration after git init.

[Wangmerlyn]

Closed as this is the same as PR #16814