dotAI: Stop returning Java stack traces from AI viewtool exceptions

Note: Part of the dotAI security review. Small hardening.

Description

CompletionsTool.handleException returns the full Java stack trace to the caller/template, unconditionally:

return Map.of("error", e.getMessage(), "stackTrace", out.toString());

There is no dev/prod gate — the trace is always built and returned whenever the viewtool throws. If a template renders that object, internal implementation details (class names, paths, stack frames) are exposed to end users (information disclosure).

Scope note: this issue covers only the stack-trace return. The separate debug logging of full prompt/response bodies (AppConfig.debugLogger) is gated behind an explicit, default-off flag (DEBUG_LOGGING / AI_DEBUG_LOGGING) and is considered working-as-intended troubleshooting behavior — out of scope here.

Affected code

• com.dotcms.ai.viewtool.CompletionsTool#handleException(Exception).

Acceptance Criteria

• The viewtool returns a generic, safe error message to the caller/template (no stack trace, no internal paths/class names).
• Full exception detail is logged server-side via Logger for diagnostics.
• Any other dotAI viewtool exception handlers that surface stack traces are updated the same way.
• Unit test: a thrown exception yields a generic error payload with no stack trace, and the detail is logged.

Priority

Low

Additional Context

Trivial change (~half a day). The debug-logging behavior is intentionally left as-is.