[SOA] Disable available-items-only search by default

[qasimikram]

What & why

New Sales Order Agent setups currently enable Search Only Available Items by default. This change disables the setting by default so the agent searches all items unless an administrator explicitly enables the availability restriction.

Linked work

Fixes AB#642623

How I validated this

• I read the full diff and it contains only changes I intended.
• I built the affected app locally with no new analyzer warnings.
• I ran the change in Business Central and confirmed it behaves as expected.
• I added or updated tests for the new behavior, or explained below why none are needed.

What I tested and the outcome

• Confirmed the default initialization now assigns false to Search Only Available Items.
• Ran git diff --check successfully.
• No automated test was added because this is a one-line default-value change and the Sales Order Agent test app is maintained outside BCApps.

Risk & compatibility

• Existing setup records are unchanged.
• Administrators can still enable Search Only Available Items.
• The behavior change applies only when default setup values are initialized.