feat(website): real logos on the Plugin Hub & homepage layout polish

[moonming]

Overview

Two related website improvements, in two commits.

1. Plugin Hub — real logos

Most plugins on /plugins/ fell back to a single grey placeholder, because giving a plugin an icon meant regenerating the iconfont sprite (static/js/plugin-icon.js) — so newer plugins were all flagged useDefaultIcon.

This decouples the icon from that sprite: a plugin can declare a logo path in plugins.json that renders as an <img> with a graceful onError fallback. No plugin shows the empty placeholder any more:

• 23 plugins now use their real brand logo (OpenTelemetry, Kafka, gRPC, GraphQL, Dubbo, OpenWhisk, OpenFunction, Elasticsearch, ClickHouse, Grafana Loki, Splunk, RocketMQ, AWS Lambda, Azure Functions, OPA, Brotli, SafeLine, OpenAPI, MQTT, Alibaba Cloud, AWS).
• The 8 built-in AI plugins share a new on-brand AI glyph (img/plugin/ai.svg).
• Other built-in plugins use the APISIX logo (img/plugin/apisix.svg) instead of the grey placeholder.
• The existing 39 sprite icons are untouched.

Logo SVGs come from each project's official assets / Devicon / CNCF artwork / gilbarbara-logos (all open-source and redistributable); each was scanned for <script> / event handlers / remote refs before adding. Plugin categories are also reordered so Traffic leads and General is last.

2. Homepage layout polish

• Integrations ("Integrates with your stack"): flatten the per-category centered rows into one dense logo wall, so rows are evenly filled instead of leaving orphan rows.
• Features ("Why APISIX?"): drop ~18rem of dead space below the heading, left over from a feature-card body this section no longer renders.
• Comparison ("Among the best"): the heading/subtitle were shifted 16.8% right by the shared .arch-head/.compare-head offset rule (duplicated in customTheme.scss and architecture.scss) while the table stayed centered. Drop the comparison classes from that rule so all three share one center axis.
• Open-source promo: stack the "Learn from developers" copy above a responsive (fluid) video instead of cramming it beside a fixed 640px player, so the text is readable.

Test plan

• Built /plugins/ and / locally — every plugin renders a real icon (0 grey placeholders); homepage sections verified at desktop and wide viewports.
• CI build / preview deploy passes.