feat(keep): add opt-in Gateway API HTTPRoute support

[somaz94]

Adds an opt-in HTTPRoute template (global.httpRoute.enabled, default false)
as a Gateway API alternative to the existing nginx Ingress, for clusters
moving off ingress-nginx (Envoy Gateway / Istio / Cilium). Closes #183.

The route mirrors the nginx ingress path layout: websocket (/websocket),
backend (/v2) and frontend (/) prefixes to their services, using a
URLRewrite ReplacePrefixMatch filter to reproduce the prefix strip. The
websocket and backend rules are gated by their .enabled flags like the
ingress template. Longer prefixes win by Gateway API path-specificity
precedence, so the frontend / rule acts as the catch-all.

Validation (helm 3.18.1 + chart-testing):

• ct lint green (yamale + yamllint + helm lint), version bumped 0.1.96 -> 0.1.97
• default render: no HTTPRoute emitted, Ingress unchanged (no regression)
• enabled render: single HTTPRoute with 3 rules, correct backendRefs/ports (6001/8080/3000)
• partial render (websocket+backend disabled): only the frontend rule

related: #183

[somaz94]

Gentle ping on this one, and on #199 alongside it. Both are opt-in and default to off, so neither changes the rendered chart unless enabled: this one adds Gateway API HTTPRoute support, #199 adds a PodDisruptionBudget. Both green. Happy to split, combine or drop either if that suits you better.