docs(plugin-dev): add "Develop a Plugin UI" guide

[fdelbrayelle]

⚠️ To be merged after 2.0

Summary

• Adds a new page plugin-developer-guide/09.plugin-ui documenting how to build custom Vue.js UI components for Kestra plugins
• Covers the Module Federation architecture, @kestra-io/artifact-sdk scaffolding, available UI slots (topology-details, log-details), vite.config.ts configuration, local dev workflow, Gradle integration, and additionalProperties

Part of: kestra-io/kestra#12696

Related PRs:

• ui-libs: feat(topology): pluggable custom action button on task nodes ui-libs#1190
• Kestra core: feat: add topology hook for task details kestra#15400

Test plan

• Page renders correctly at /docs/plugin-developer-guide/develop-a-plugin-ui
• Appears in the Plugin Developer Guide sidebar after "Build and Publish a Plugin"
• All code blocks have correct syntax highlighting
• Links to artifact-sdk repo resolve

[github-actions]

☁️ Cloudflare Worker Preview Deployed!

🔗 https://ks-docs-plugin-ui-developer-guide-docs.kestra-io.workers.dev
🔗 https://d0a94ee0-docs.kestra-io.workers.dev

## 🔦 Lighthouse Benchmark

Tested: https://ks-docs-plugin-ui-developer-guide-docs.kestra-io.workers.dev on 2026-04-15 08:09 UTC
Compared against main baseline from 2026-04-10

Scores (0–100, higher is better)

Page	Performance	Accessibility	Best Practices	SEO
Home	60	79	59	92
Pricing	98	88	59	100
Enterprise	94 🟢 +10	78	59	100
Cloud	89	83	59	100
About Us	99	87	59	100
Docs Landing	84	84	59	92
Contribute to Kestra (simple docs)	97	84	59	92
Flow (full featured docs)	96	86	59	92
Blog Index	65 🔻 -16	86	59	100
Blog Post (sample)	88	83	59	100
VS Page (sample)	97	88	59	100
Plugins Landing	92	77	59	92
Plugin Page (sample)	97	87	59	100
Plugin Debug Page (sample)	96	87	59	100
Plugin Debug Return Page (sample)	96	87	59	100
Blueprints Landing	93	77	56	92
Blueprint Audit Logs CSV Export	69	82	59	100

Core Web Vitals (lower is better)

Page	LCP	FCP	TBT	CLS	Speed Index
Home	1.85 s 🟢	1.05 s 🟢	463 ms 🔻	0.000	5.81 s 🟢
Pricing	1.07 s	0.59 s	49 ms	0.000	0.79 s
Enterprise	1.54 s	0.79 s	46 ms 🔻	0.003	1.03 s 🟢
Cloud	2.11 s	0.51 s	70 ms 🔻	0.000	0.77 s
About Us	0.91 s 🟢	0.56 s	62 ms	0.000	0.85 s
Docs Landing	2.71 s 🔻	0.64 s 🟢	96 ms 🟢	0.000	1.08 s
Contribute to Kestra (simple docs)	0.95 s	0.49 s 🟢	134 ms 🔻	0.000	0.69 s 🟢
Flow (full featured docs)	0.86 s 🟢	0.58 s 🟢	134 ms	0.000	1.03 s
Blog Index	7.68 s 🔻	0.52 s 🟢	58 ms	0.001	17.67 s 🔻
Blog Post (sample)	2.26 s 🔻	0.53 s	47 ms	0.000	0.74 s
VS Page (sample)	1.14 s	0.59 s	60 ms	0.000	0.92 s
Plugins Landing	1.13 s 🟢	0.52 s	125 ms 🔻	0.000	2.15 s 🔻
Plugin Page (sample)	0.98 s	0.52 s	23 ms	0.051	1.46 s
Plugin Debug Page (sample)	0.97 s	0.53 s	82 ms	0.001	1.57 s
Plugin Debug Return Page (sample)	0.92 s 🟢	0.50 s	86 ms	0.025	1.68 s
Blueprints Landing	1.30 s	0.71 s	10 ms 🟢	0.000	1.90 s
Blueprint Audit Logs CSV Export	0.96 s 🟢	0.53 s	184 ms	0.485	1.94 s

Legend

🟢 improved  ·  🔻 regressed  ·  (blank) no significant change
Score threshold: ±10 pts  ·  Metric threshold: ±30% of baseline

[aj-emerich]

LGTM