Use Yarn and add Telegram webhook setup

[NeverBehave]

Summary

• pin Yarn 4.5.0 through Corepack and use yarn.lock as the only lockfile
• configure Yarn with the node-modules linker for Wrangler
• add a build script so Cloudflare's existing yarn run build command succeeds
• add tested commands to set, inspect, and delete the Telegram webhook
• document Yarn build/deploy settings and webhook registration

Webhook commands

• yarn webhook:set [worker-url]
• yarn webhook:info
• yarn webhook:delete

Verification

• yarn install --immutable
• yarn test (15 tests)
• yarn run build
• yarn deploy --dry-run

[Copilot]

Copilot review overview

🟡 Changes recommended

Update the supported Node.js/Corepack guidance for Node.js 25.

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Review effort: Lite
Findings: 1

Open (1)

• Yarn setup fails on supported Node.js 25 without Corepack · New

What changed in this PR

Migrates Cloudflare Workers builds from npm to Yarn 4.5.0.

Changes:

• Pins Yarn through Corepack and configures the node-modules linker.
• Replaces package-lock.json with yarn.lock.
• Adds build/deployment scripts and documents Yarn workflows.

File	Summary
yarn.lock	Adds the Yarn dependency lockfile.
README.md	Documents Yarn and Workers workflows; Corepack guidance must address Node.js 25.
package.json	Pins Yarn and adds build/deployment scripts.
package-lock.json	Removes the npm lockfile.
.yarnrc.yml	Configures the node-modules linker.
.gitignore	Ignores Yarn-generated metadata.

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