chore - disable autoupdate in install-flex config

[lgarceau768]

Summary

• Set autoupdate: false in the opencode.json written by install-flex
• Prevents the upstream version-check dialog from appearing on every session start in the Flexion fork, since our custom build will always appear outdated relative to the upstream npm release

Changes

• install-flex: added "autoupdate": false to the generated ~/.config/opencode/opencode.json

Test Plan

• Run install-flex on a fresh machine and verify ~/.config/opencode/opencode.json contains "autoupdate": false
• Launch opencode-work and confirm no version-check dialog appears on session start

[github-actions]

Hey! Your PR title chore - disable autoupdate in install-flex config doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

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