Add kubectl namespace flag generator tests (APP-3476)

[lucieleblanc]

Description

Add tests for kubectl generator namespace forwarding with various token orderings.

These tests confirm that kubectl_script() correctly extracts and forwards the --namespace value regardless of where -n/--namespace appears in the token list:

• Before the subcommand: kubectl -n kube-system get pods
• After the subcommand: kubectl get -n kube-system pods
• With multiple flags: kubectl --context staging -n project1 get pods
• Using equals syntax: kubectl --namespace=kube-system get pods

The generators already handle all these orderings correctly — the actual completion engine fix is in warp-internal: https://github.com/warpdotdev/warp-internal/pull/24138

What the warp-internal PR fixes

The completion engine's subcommand lookup had two bugs:

1. Legacy path: Used s.contains(token) to match options, which caused false positives (e.g., --no-headers matching -n). Fixed to use exact match.
2. V2 path: deepest_matching_subcommand_signature didn't skip flags when searching for subcommands, so kubectl -n kube-system get never reached the get subcommand. Fixed by adding flag-aware iteration.

See: GitHub #3929

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Conversation: https://staging.warp.dev/conversation/5f0b6b65-3d5f-44e2-9620-e0fee969057c
Run: https://oz.staging.warp.dev/runs/019d6e0c-0f31-74e9-8d56-646aa96f1f22
This PR was generated with Oz.

[linear]

APP-3476 [kubectl] Fix -n/--namespace flag breaking subsequent resource completion

When flags like -n or --namespace come before the subcommand, subsequent resource completion falls back to file listing instead of querying the cluster.

Confirmed still repro'd — workaround is reordering flags. The kubectl_script() helper in command-signatures/src/generators/kubectl.rs already forwards --namespace from tokens, but the parser may not handle all token orderings correctly.

See GitHub #3929