refactor(template): rename startup-landing-page → saas-landing-page

The template's redesigned content (around fictional Beacon - a B2B SaaS feedback platform)

What's renamed (internal only):
- templates/startup-landing-page/ → templates/saas-landing-page/
- hugoblox.yaml: template id "landing-page" → "saas-landing-page",
  name "Landing Page" → "SaaS Landing Page"
- CI workflows: source path in ci-build-starters-matrix.yml and
  release-package-splitter.yml
- README.md: slug in URLs, CLI command (`npx hugoblox
  create site --template saas-landing-page`)
- splitter target repo: hugo-theme-startup-landing-page →
  hugo-theme-saas-landing-page

.github/workflows/ci-build-starters-matrix.yml

@@ -69,8 +69,8 @@ jobs:
                 starter:
                     - name: academic-cv
                       path: templates/academic-cv
-                    - name: startup-landing-page
-                      path: templates/startup-landing-page
+                    - name: saas-landing-page
+                      path: templates/saas-landing-page
                     - name: dev-portfolio
                       path: templates/dev-portfolio
 

.github/workflows/release-package-splitter.yml

@@ -60,7 +60,7 @@ jobs:
                     ["templates/data-science-blog"]="hugo-theme-data-science-blog"
                     ["templates/documentation"]="hugo-theme-documentation"
                     ["templates/link-in-bio"]="hugo-theme-link-in-bio"
-                    ["templates/startup-landing-page"]="hugo-theme-startup-landing-page"
+                    ["templates/saas-landing-page"]="hugo-theme-saas-landing-page"
                     ["templates/dev-portfolio"]="hugo-theme-developer-portfolio"
                     ["templates/markdown-slides"]="hugo-theme-markdown-slides"
                     ["templates/starter"]="hugo-starter"