fix(tasks): use .jsdoc.json with build/esm/src for ESM doc generation - #9522

Summary

Fixes the failing npm run docs / pnpm run docs JSDoc generation for @google-cloud/tasks (currently the only generated GAPIC package in packages/ with "type": "module" / esm: true):

1. package.json "docs" script: packages/google-cloud-tasks/package.json previously referenced .jsdoc.js ("docs": "jsdoc -c .jsdoc.js"), which no longer existed after the ESM migration (package.json is listed in default.keep in librarian.yaml).
2. JSDoc config format (.jsdoc.json): jsdoc (cli.js) only uses require() when path.extname(confPath) === '.js'; for all other extensions (.cjs, .json, etc.), it reads the file as text and runs JSON.parse(stripJsonComments(...)). As a result, .jsdoc.cjs with module.exports = { ... } fails with SyntaxError: Unexpected token 'm' ... is not valid JSON, while .jsdoc.js inside a "type": "module" package returns an empty module namespace from require(). Switching to .jsdoc.json (matching handwritten/storage/.jsdoc.json) resolves this cleanly.
3. source.include path: Dual ESM/CJS packages compile .js sources to build/esm/src (rather than build/src). Updated source.include to ["build/esm/src", "protos"] so JSDoc locates the compiled ESM sources.

A companion PR updates the ESM template and baselines in core/generator/gapic-generator-typescript so future generations emit .jsdoc.json directly.

Verification

• Ran pnpm run compile and pnpm run docs in packages/google-cloud-tasks and verified ./docs is generated cleanly with exit code 0.