chore: update all packages to latest, migrate ESLint to v9 flat config

[Copilot]

Brings all dependencies current, eliminates 18 vulnerabilities (13 high), and modernizes the ESLint setup to v9 flat config.

Package upgrades

Area	Change
React	18 → 19 (react, react-dom, @types/*)
ESLint	8 → 9 + @typescript-eslint 6 → 8
Security	axios 1.12 → 1.15, webpack 5.99 → 5.106
Figma	@figma/plugin-typings 1.116 → 1.124, eslint-plugin-figma-plugins 0.16 → 1.0
Misc	typescript 5.3 → 5.9, framer-motion 12.23 → 12.38, tailwindcss 3.4.17 → 3.4.19, all other minor/patch bumps

Added: typescript-eslint (unified package) + @eslint/js — required for ESLint v9 flat config.

ESLint v9 flat config migration

• Removed eslintConfig from package.json
• Created eslint.config.mjs using tseslint.config() with file-scoped rules (TS/TSX source only) and a separate CommonJS globals block for webpack.config.js / postcss.config.js
• Added lint script to package.json

Code fixes (surfaced by stricter lint rules)

• any elimination: figmaStorage.ts (any → unknown/Record<string,unknown>), useFigmaMessaging.ts generic default (unknown|any → Record<string,unknown>), all demo components now use the FigmaMessage type instead of (message: any)
• pluginController.ts: wrapped case blocks in braces (no-case-declarations), let → const for non-reassigned variables, any[] → ReturnType<typeof getNodeProps>[]
• CreateSpiralApp.tsx: e.target.value as any → as typeof shape