Gate x-callback recall to exportable memories

[bob-codedaptive]

Motivation

• The x-callback-url recall route allowed unauthenticated callers to invoke moot_memory_search and receive non-public memory previews and IDs because no public/exportable filter was enforced.
• The change enforces the same public/exportable privacy gate used by the App Intent path so that cross-app callbacks cannot leak private/default memories.

Description

• Force filter = "exportable" for inbound x-callback-url recall requests in MootURLRouter.route(_:using:) before calling the substrate, overriding any caller-supplied filter.
• Add a regression test recall verb forces exportable filter before routing to IntentToolCallTests.swift that seeds a private default drawer and a public drawer then asserts the x-callback recall only returns the public/exportable drawer.
• Preserve existing verb allowlist and callback-scheme gating; the change only applies to the recall verb routing logic.

Testing

• Ran git diff --check to validate whitespace and basic diffs (passed).
• Added and ran the URL router regression test group via swift test --filter URLRouterTests, but the test run was blocked by SwiftPM dependency fetch failures (HTTP 403 CONNECT tunnel errors) in the execution environment, so repository unit tests could not be fully executed here.
• The new unit test exercises the router against the in-memory TestBridge and is included for CI to validate in a network-enabled environment.

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Codex Task

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[bob-codedaptive]

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