chore(deps): ESLint 9 flat config, Zod 4, drop Storybook

[gaspb]

Lands the remaining open Dependabot updates after #1155. The security-relevant deps (postcss, ajv, vite) were already current on main, so #1162/#1090/#941 are superseded; this applies the breaking upgrades from #1161/#1160 that were deferred.

ESLint 9 + flat config:

• eslint 8->9.39, typescript-eslint 6->8.61, eslint-config-prettier 8->10, eslint-import-resolver-typescript 3->4, eslint-plugin-react-hooks 4->7, eslint-plugin-unused-imports 3->4
• rewrite eslint-config-meteroid as a flat config (index.mjs), consumed via eslint.config.mjs in web-app and ui; remove legacy .eslintrc/.eslintignore
• pinned ESLint 9, not 10: eslint-plugin-react 7.37 only supports up to eslint ^9.7
• restore prior lint strictness where typescript-eslint v8 newly errors (no-unused-expressions, caught-error vars, empty object types); import/namespace disabled as redundant with tsc

Zod 3 -> 4 (+ @hookform/resolvers 3 -> 5):

• migrate app schemas/forms: required_error -> error, drop hand-written zod-3 internal type annotations, forward sub-parse issues, fix useZodForm/useForm input-vs-output typing
• keep the vendored znv env parser on the zod/v3 compat export (relies on zod-3 internals; isolated to @md/common + web-app/lib/env.ts)

Dev tooling: @commitlint 18->21, @manypkg/cli 0.21->0.25, dotenv-cli 7->11, turbo 2.9.14->2.9.18

Drop Storybook: unused (no stories, no config, no scripts) — removes all @storybook/*, storybook, chromatic, concurrently from @md/ui.

Description

[Provide a brief description of the changes introduced by this pull request and the motivation behind them.]

Checklist

• The code follows the project's coding conventions and style guidelines.
• All tests related to the changes have passed successfully.
• Documentation has been updated to reflect the changes (if applicable).
• All new and existing unit tests have passed.
• I have self-reviewed my code and ensured its quality.
• I have added/updated necessary comments to aid understanding.