feat(tekton): add Tekton Pipelines eval tasks

[ksimon1]

feat(tekton): add Tekton Pipelines install/uninstall/status Makefile targets and eval tasks

This PR introduces a new tekton eval set to kubernetes-mcp-server, exposing domain-specific Tekton operations.

[waveywaves]

Nice addition. The eval tasks are well-structured and the Makefile targets follow the existing kubevirt pattern. Since this lands before #892 (the tekton toolset implementation), a couple things to clean up:

1. Forward references to the tekton toolset: The Makefile and README reference the tekton toolset and its tools (tekton_pipeline_start, etc.) which won't exist until #892 merges. The eval tasks themselves work fine via the core toolset's resources_* tools, but the docs will be misleading in the window between this merging and #892 merging. Either remove the forward references or add a note like "requires #892 for dedicated tekton tools, works with core toolset in the meantime."

2. Setup script duplication: The 20-line namespace cleanup/wait loop is identical across all 9 tasks (~180 lines of duplication). Would be worth extracting to helpers/cleanup-namespace.sh like kubevirt does with helpers/verify-vm.sh.

[ksimon1]

@waveywaves thanks for the review. Your comments should be resolved now