chore: update JavaScript linters to modern versions

[jonpspri]

Supports updates to admin console as A2A and other components are modernized.

Summary

• Upgrade ESLint from v8 to v9 (major version update)
• Replace deprecated eslint-config-standard with neostandard for modern JavaScript linting
• Move JS linter dependencies from inline Makefile installation to package.json for better dependency management
• Add htmlhint and retire to tracked devDependencies

Test plan

• Run make install-web-linters to verify dependencies install correctly
• Run JS linting targets to verify ESLint v9 compatibility
• Verify no regressions in existing lint checks

[Copilot]

Pull request overview

This pull request updates JavaScript linting infrastructure by upgrading ESLint from v8 to v9 and consolidating dependency management. The changes replace the deprecated eslint-config-standard with neostandard, move linter installations from inline Makefile npm commands to package.json devDependencies, and simplify the installation process.

Key changes:

• ESLint upgraded from ^8.57.1 to ^9.39.0 (major version upgrade)
• Replaced eslint-config-standard with neostandard ^0.12.2
• Consolidated web linting tools (htmlhint, retire) in package.json

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 3 comments.

File	Description
package.json	Updated ESLint to v9, added neostandard, htmlhint, and retire to devDependencies; removed eslint-config-standard; downgraded @stylistic/eslint-plugin to 4.0.0
Makefile	Simplified install-web-linters target to use npm install instead of inline installation commands

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 7 changed files in this pull request and generated 4 comments.

Comments suppressed due to low confidence (1)

Makefile:2454

• The npx commands in the lint-web target (lines 2448, 2450, 2452, 2454) are missing the '--yes' flag, which is inconsistent with the other Makefile targets (jshint, jscpd, markuplint, format-web) that use 'npx --yes'. Without the '--yes' flag, npx will prompt for user confirmation if packages need to be installed, which could cause the target to hang in automated environments. Add '--yes' to these npx invocations for consistency.

	@find mcpgateway/templates -name "*.html" -exec npx htmlhint {} + 2>/dev/null || true
	@echo "🔍 Linting CSS files..."
	@find mcpgateway/static -name "*.css" -exec npx stylelint {} + 2>/dev/null || true
	@echo "🔍 Linting JS files..."
	@find mcpgateway/static -name "*.js" -exec npx eslint {} + 2>/dev/null || true
	@echo "🔒 Scanning for known JS/CSS library vulnerabilities with retire.js..."
	@cd mcpgateway/static && npx retire . 2>/dev/null || true

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[crivetimihai]

Fixes applied to the PR:

1. Added eslint to .PHONY declaration - was missing for the new target
2. Fixed eslint target - changed from npm install --save-dev (which modified package files) to @npm install --no-save
3. Added @ prefix to commands for silent output consistency
4. Removed redundant npm install from lint-web target (eslint already handles it)
5. Restored install-web-linters target - provides explicit install command using package.json dependencies

Rebased onto current main (5 new commits integrated, no conflicts).