feat(common): add nanoid-based ID generators

[brunozoric]

Summary

• Adds nanoid-based ID generators to @webiny/stdlib (common slice), ported from webiny-js-v6/packages/utils/src/generateId.ts
• Six generators: generateId, generateAlphaNumericId, generateAlphaNumericLowerCaseId, generateAlphaId, generateAlphaLowerCaseId, generateAlphaUpperCaseId
• All accept an optional size parameter (default 21 characters)
• New dependencies: nanoid (v5), nanoid-dictionary (v5)

Usage

import {
    generateId,
    generateAlphaNumericId,
    generateAlphaNumericLowerCaseId,
    generateAlphaId,
    generateAlphaLowerCaseId,
    generateAlphaUpperCaseId
} from "@webiny/stdlib";

generateId();            // URL-safe: "V1StGXR8_Z5jdHi6B-myT"
generateId(10);          // custom size: "V1StGXR8_Z"
generateAlphaNumericId();         // A-Z a-z 0-9
generateAlphaNumericLowerCaseId(); // a-z 0-9
generateAlphaId();                // A-Z a-z
generateAlphaLowerCaseId();       // a-z
generateAlphaUpperCaseId();       // A-Z

What changed

File	Change
src/common/utils/generateId/generateId.ts	Implementation (copied from v6)
src/common/utils/generateId/index.ts	Barrel export
src/common/utils/generateId/README.md	Feature docs with API table and usage examples
src/common/index.ts	Re-exports all six generators from @webiny/stdlib
__tests__/generateId.test.ts	23 tests covering default size, custom size, character set validation, uniqueness
AGENTS.md	Added generateId to @webiny/stdlib package contents
README.md	Added row to Common features table
src/common/utils/README.md	Added row to utils index
package.json / yarn.lock	Added nanoid + nanoid-dictionary

Test plan

• 401 tests passing (378 baseline + 23 new), zero failures
• Full pre-commit chain clean (yarn && yarn adio && yarn format:fix && yarn lint:fix && yarn typecheck && yarn build && yarn test:coverage)
• No regressions in existing tests
• Coverage: 96.52% statements, 93.44% branches