Fix: Update bun.lock and remove package-lock.json

From the PR description

Problem

The Railpack build was failing with "lockfile had changes, but lockfile is frozen" because commit 13e47ea added cheerio, openai, helmet, node-cache, stripe, and zod to backend/package.json but only updated backend/package-lock.json (npm's lockfile) - not backend/bun.lock. Railpack detects Bun as the package manager and runs bun install --frozen-lockfile, which fails because the Bun lockfile is missing the new dependencies and their transitive packages.

Solution

Updated backend/bun.lock to add all missing packages to the workspace dependencies/devDependencies section and added all new package entries (cheerio, openai, helmet, node-cache, stripe, zod, @types/node-cache, and their transitive dependencies) with correct versions and integrity hashes sourced from the npm lockfile. Also deleted backend/package-lock.json to eliminate the conflicting npm lockfile - since the project uses Bun, only bun.lock should be present to prevent future mismatches.

Changes

• Modified backend/bun.lock
• Deleted backend/package-lock.json

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