Fix pre-existing issues in gateway-api form components

[R-Lawton]

context

these issues existed in the original gateway-api-console-plugin and were carried over during the merge (#636, #690). they're not regressions — they were in the source code before the merge.

issues

port input validation

• GatewayCreatePage.tsx: clearing the port field yields NaN (parseInt('', 10)) which shows in the form and YAML
• FilterActions.tsx: mirror port field accepts non-numeric text and emits NaN

filter validation gaps

• FilterActions.tsx: add/set rows with empty header values are silently dropped — gateway API permits empty header values
• filterUtils.tsx: header-modifier validation accepts blank rows, empty filters can be saved

httproute form

• HTTPRouteCreatePage.tsx: positional path splitting (pathSplit[5]) couples to URL shape — should use useParams()
• HTTPRouteCreatePage.tsx: parent references without sectionName silently dropped, but sectionName is optional in gateway API spec
• HTTPRouteRuleWizard.tsx: method dropdown omits HEAD, CONNECT, OPTIONS, TRACE — routes with those methods show no matching option

filterUtils typing

• filterUtils.tsx: ~10 instances of any type without justification — should use exported filter type definitions
• filterUtils.tsx: as HTTPRouteFilter[] cast masks shape mismatch, .filter(Boolean) is a no-op
• filterUtils.tsx: getFilterSummary returns untranslated user-facing text

useHTTPRouteActions

• useHTTPRouteActions.tsx: actions reported as loaded before model resolves — edit/delete flash for unauthorized users

types

• types.ts: pathType/method widened to string instead of reusing literal unions from HTTPRouteResource