Add stable instance identity to NavigationManager

[marioserrano09]

Part of #107.

Problem

There is no stable, framework-agnostic identifier correlating a NavigationManager instance to "which tab/iframe/desktop" it belongs to. This is needed to:

• Correlate a ZKNavigationManager instance with the navigation token used to fix the NavigationManagerSession race (Replace NavigationManagerSession session-scope with ThreadLocal #108).
• Support a future session-level registry of active navigation manager instances (Add stable instance identity to NavigationManager #109).
• Aid debugging/logging when multiple concurrent managers exist in one session.

Change

• Add an id (e.g. String getId()) to the NavigationManager interface, generated on creation, independent of any ZK type (Desktop, etc.) — core navigation module must stay UI-framework-agnostic.
• Implement in BaseNavigationManager (generate a random/opaque id at construction).
• ZKNavigationManager may optionally expose the ZK Desktop id as a convenience, but the core contract must not depend on it.

Affected files

• platform/core/navigation/src/main/java/tools/dynamia/navigation/NavigationManager.java
• platform/core/navigation/src/main/java/tools/dynamia/navigation/BaseNavigationManager.java
• platform/ui/zk/src/main/java/tools/dynamia/zk/navigation/ZKNavigationManager.java

[marioserrano09]

Implemented on branch feat/navigation-multi-desktop-support (commit 2a4246e): added NavigationManager#getId(), implemented in BaseNavigationManager as a UUID generated once at construction. Framework-agnostic, no ZK dependency.

[marioserrano09]

Implemented on feat/navigation-multi-desktop-support (commits 2a4246e, 0b2b831); PR #112. Will close with the PR.

[marioserrano09]

Implementado y mergeado en #112 (cd0e6dd en main). Cerrado. Pendiente a nivel épica (#107): validación contra dynamia-erp con login real de Spring Security y documentar el contrato de hand-off en docs/backend/.