CHORE: Remove Tekton CI/CD platform

- Delete tekton/ directory (pipeline, triggers, dashboard, ci-cd)
- Remove tekton references from kustomization.yaml
- Switching to GitHub Actions for CI/CD

tekton/ci-cd/manifests/pipelines/fastapi-pipeline.yaml

@@ -1,59 +0,0 @@
-apiVersion: tekton.dev/v1
-kind: Pipeline
-metadata:
-  name: fastapi-build-deploy
-  namespace: tekton-pipelines
-spec:
-  description: Build FastAPI app and push to Zot registry
-  params:
-    - name: git-url
-      description: Git repository URL
-      type: string
-    - name: git-revision
-      description: Git revision (branch/tag/sha)
-      type: string
-      default: main
-    - name: app-name
-      description: Application name
-      type: string
-    - name: context-dir
-      description: Docker build context directory
-      type: string
-      default: ./fastapi
-  workspaces:
-    - name: shared-workspace
-      description: Shared workspace for all tasks
-    - name: docker-credentials
-      description: Docker registry credentials
-  tasks:
-    - name: clone
-      taskRef:
-        name: git-clone
-      params:
-        - name: url
-          value: $(params.git-url)
-        - name: revision
-          value: $(params.git-revision)
-        - name: deleteExisting
-          value: "true"
-      workspaces:
-        - name: output
-          workspace: shared-workspace
-
-    - name: build-push
-      taskRef:
-        name: buildah-build-push
-      runAfter:
-        - clone
-      params:
-        - name: IMAGE
-          value: zot0213.kro.kr/$(params.app-name):$(params.git-revision)
-        - name: DOCKERFILE
-          value: ./Dockerfile
-        - name: CONTEXT
-          value: $(params.context-dir)
-      workspaces:
-        - name: source
-          workspace: shared-workspace
-        - name: dockerconfig
-          workspace: docker-credentials