Add 400 input-validation responses to read/delete operations

[clundie-CL]

Problem description

The new CAMARA Validation Framework run on PR #131 raised 14 owasp:api8:2023-define-error-validation warnings (rule S-318) against code/API_definitions/network-access-management.yaml. Despite the rule's message ("Missing error response of either 400, 422 or 4XX"), it specifically requires a 400 or 422 input-validation error response — the existing 401/403/404 don't satisfy it because they're auth/resource errors, not input validation.

All affected operations are GETs and DELETEs that accept path or query parameters (UUID-typed {trustDomainId}, {deviceId}, {rebootRequestId}, etc.) which can fail format validation before auth/resource checks run.

Affected operations:

Path	Method	Line
/services	GET	215
/services/{serviceId}	GET	260
/trust-domains/capabilities	GET	300
/trust-domains	GET	387
/trust-domains/{trustDomainId}	GET	425
/trust-domains/{trustDomainId}	DELETE	496
/trust-domains/{trustDomainId}/devices	GET	575
/trust-domains/{trustDomainId}/devices/{deviceId}	GET	611
/trust-domains/{trustDomainId}/devices/{deviceId}	DELETE	680
/network-access-devices	GET	705
/network-access-devices/{networkAccessDeviceId}	GET	736
/reboot-requests	GET	842
/reboot-requests/{rebootRequestId}	GET	874
/reboot-requests/{rebootRequestId}	DELETE	942

Expected action

For each operation, add a '400' response entry referencing the shared Generic400:

'400':
  $ref: '../common/CAMARA_common.yaml#/components/responses/Generic400'

Mechanical fix; single file (code/API_definitions/network-access-management.yaml); ~14 small additions. Can land as one PR.

Additional context

• Source: PR Sync common files from Commonalities r4.2 #131 validation run, workflow run 25749712191. All 14 findings are warnings, not blockers — the alpha cut is not gated.
• Related: Document empty-list, 400/422, and GENERATE credential conventions #129 — the 400-vs-422 boundary (which class of input error triggers which code) is the deeper documentation question. This issue is the more basic prerequisite: every read/delete should have a 400 at all.