test: drop redundant tests, render each page once, run SSR only in the ssr group

[datlechin]

• LastModified reads git log once per run instead of once per URL: a sitemap was 739 git processes (6.9s), now one (0.2s). Same lastmod for all 740 URLs.
• SSR is off in tests. requireSsr() turns it on, probes the service once per process, and makes a failed render throw instead of falling back to the client shell.
• Tests that need SSR, the built bundle or node_modules sit in ->group('ssr'); requireSsr() / requireSsrJob() fail a test that isn't in it. The php job runs --exclude-group=ssr, the ssr job --group=ssr.
• The registry is crawled once for props and once for SSR (seoCrawlProps(), seoCrawlHtml() in Seo/helpers.php), down from about ten crawls of 749 URLs.
• The real-site sitemap is generated once per run (seoCommittedSitemap()).
• Each page is rendered once per test file where several tests rendered it again (PageFrame, SiteChrome, Compare, Databases, Features, Pricing, About, Blog, Download, iOS).
• Locale datasets cut to en + vi where the behaviour does not depend on the locale.
• Tests whose assertions already exist in another test are removed or merged into it.
• DeployScriptTest shares sandbox runs: 14 full runs down to 7, plus 3 that skip the git setup.
• BannedClaims, Wording, ContentParity and AssetManifest build their regexes, rule lists and fixtures once.
• Comment blocks cut to one-line reasons.
• 2624 → 2127 cases. CI test step: php 162s → 52s, ssr 250s → 40s. Peak memory fits the default 512M.