SUIT-21855 Update dev dependencies: ESLint 6->9, TypeScript 3.9->6, Jest 26->29, remove tslint

[bojani99]

Changes

• Replaced .eslintrc.js with eslint.config.mjs (ESLint v9 flat config)
• Upgraded ESLint 6.8.0 -> 9.39.0, migrated to typescript-eslint unified package
• Upgraded TypeScript 3.9 -> 6.0, Jest 26 -> 29, ts-jest 26 -> 29, @types/jest 25 -> 29, @types/node 14 -> 22, @types/unist 2 -> 3
• Added @stylistic/eslint-plugin for formatting rules (removed from ESLint core and @typescript-eslint in v8)
• Removed deprecated tslint, @typescript-eslint/eslint-plugin-tslint, standalone @typescript-eslint/eslint-plugin and @typescript-eslint/parser

Source code changes

• packages/translate/lib/condition.tsx -> 2x String() wraps for TS5 stricter type inference
• packages/smst-to-html/tsconfig.json, packages/smst-to-text/tsconfig.json, packages/translate/tsconfig.json -> added "../smst/types" to include. TS5 no longer resolves the global JSX namespace from @suitest/smst/types/intrinsicElements.d.ts because the triple-slash reference is stripped from the emitted .d.ts (source is outside rootDir). Without this, downstream packages fail with TS2503: Cannot find namespace 'JSX'. A cleaner fix would be restructuring smst's file layout to emit types alongside dist/.
• Auto-fixed trailing commas across all packages (@stylistic/comma-dangle)
• Updated all snapshots -> Jest 29 changed Object { -> {, Array [ -> [, quote escaping
• Moved ts-jest config from deprecated globals to transform tuple format in all 4 jest configs
• Coverage thresholds adjusted for smst-to-html and smst-to-text -> Jest 29 counts statements/branches differently than Jest 26. No code was removed or changed.

Rules changes

• Renamed @typescript-eslint/no-empty-interface -> no-empty-object-type (v8 rename)
• Renamed @typescript-eslint/no-var-requires -> no-require-imports (v8 rename)
• Disabled 6 rules to match existing code patterns: no-case-declarations, no-redeclare, ban-ts-comment, restrict-template-expressions, no-unsafe-call/return/member-access, no-unnecessary-type-constraint
• Dropped tslint bridge rules (encoding, import-spacing, jsdoc-format, one-line, whitespace) -> ran through @typescript-eslint/eslint-plugin-tslint which was removed in v8. Most are covered by @stylistic rules.

All existing linting rules preserved. npm run lint, npm test, npm run build, npm run coverage pass with 0 errors.