docs(site): label roadmap features on the landing page

[kannandreams]

Two features on the landing page carried a live status with no implementation behind them:

Claim	Reality in src/glyf/
"Visual diff as a build artifact" — side-by-side diff against the previous build	No match for visual_diff / visual-diff anywhere.
"Pipeline hooks and alerts" — Slack/webhook alerts with severity-based routing	dashboard/macros/alert.py is a UI banner component (info / success / warning). No Slack, no webhooks, no routing.

Re-badging alone would have changed nothing

item.status was never rendered. All ten values were dead data, and the .featureStatus / .featureStatus--roadmap CSS was orphaned from an earlier layout — so every feature looked equally shipped regardless of its status string.

So this does three things:

1. Renders the badge for roadmap items, reusing the existing CSS. .featureStoryName becomes a flex row to seat it next to the name.
2. Fixes the prose, which is the part a visitor actually reads. Every roadmap description moves to the future tense — including the three that were already correctly badged (coming soon / soon) but still written in the present tense.
3. Normalises the vocabulary: three values (live, coming soon, soon) for two concepts becomes live and roadmap.

Also drops a ✓ visual diff → artifacts/diff.html line from the git-diff mockup, which sat inside a shipped feature and asserted an unshipped one.

What is deliberately kept

The mockup visuals for roadmap items. With a Roadmap badge on the item and future-tense copy, they read as previews rather than claims — which is what they are.

Verified against the production build

Roadmap badges rendered: 5
  ROADMAP  Visual diff as a build artifact
  ROADMAP  Pipeline hooks and alerts
  ROADMAP  Generated React components
  ROADMAP  Agent-ready MCP server
  ROADMAP  Natural language chart edits
  live     dbt ref() in every chart
  live     Zero-server static output

All four old claim strings are absent from the built HTML. npm run build succeeds.

docs/integrations/overview.md already listed Slack/webhook alerting under "Planned integration areas" and needed no change — the docs were honest; only the landing page was not.