ci: resolve Trunk Prettier plugin dependencies

[KooshaPari]

Summary

• install Trunk-managed tools before the repository setup hook completes
• install the declared Svelte and Tailwind Prettier plugins into Trunk's isolated Prettier tool directory
• keep the Trunk workflow single-install and format the setup action/workflow YAML

Evidence

• actionlint v1.7.8 targeted workflow
• frontend-rooted Prettier check for both changed YAML files and frontend/web
• git diff --check

Stacked on PR #323; no merge performed.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[github-actions]

Legacy Tooling Scan Report

Severity	Count
Critical	0
High	0
Medium	0
Low	0

No violations detected.

This is a WARN-mode scan. Fix before strict enforcement begins.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

📊 Tier-2 Coverage Gate Results

Tier	Threshold	Status
Rust lib (byteport-transport)	≥71%	✅ Pass
Go framework (backend)	≥70%	✅ Pass
Frontend unit (frontend/web)	≥60%	✅ Pass