chore: replace tsup bundle with plain tsc emit

[dopry]

Follow-up to #24. Now that the package is ESM-only, the reasons tsup was adopted in Phase 3 (dual CJS+ESM output, bundled .d.ts rollup) no longer apply — so this removes the bundler instead of maintaining it.

Changes

• Build: npm run build now runs tsc -p tsconfig.build.json (new config extending tsconfig.json with noEmit: false, outDir: dist, rootDir: src). dist/ mirrors src/ with per-module .js / .d.ts / .js.map instead of a single bundle.
• Removed: tsup devDependency and tsup.config.ts.
• Unchanged for consumers: entry points stay dist/index.js / dist/index.d.ts, so main, types, and the exports map are untouched, and the exports map continues to block deep imports into internals. Docker (node dist/index.js) unchanged.
• Test: esm-package.spec.ts builds via tsc (shell-free, cross-platform) and still verifies the built package loads under real Node ESM through the exports map with no empty side-effect imports — now checking every emitted module rather than one bundle.

Why

• The emitting compiler is the same one that typechecks (nodenext + verbatimModuleSyntax), so the published output can never drift from what tsc verified — and the declaration rollup step (historically the fragile part of bundler-based library builds) is gone.
• Mirrored dist makes future subpath exports (@dopry/pecans/backends, …) a one-line exports addition.
• Consumer stack traces point at real module files; one less toolchain in devDependencies.

Verified: lint, prettier, typecheck, full vitest suite (771 tests), node dist/index.js server start, and a real-Node import('@dopry/pecans') smoke test.

🤖 Generated with Claude Code

https://claude.ai/code/session_017zXcPSv6FFTPgD59T4KudM

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Generated by Claude Code

[Copilot]

Pull request overview

This PR removes the tsup bundling step and switches the package build to a plain TypeScript compiler emit (tsc -p tsconfig.build.json), producing a dist/ tree that mirrors src/ for the ESM-only package.

Changes:

• Replace the tsup build with tsc using a dedicated tsconfig.build.json.
• Remove tsup configuration and dependency.
• Update the ESM package integration test to build with tsc directly and validate emitted modules.

Reviewed changes

Copilot reviewed 5 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tsup.config.ts	Removes the tsup bundler configuration.
tsconfig.json	Stops including the removed tsup.config.ts in the main TS project.
tsconfig.build.json	Adds a build-specific TS config to emit dist/ from src/.
test/integration/esm-package.spec.ts	Builds via tsc and validates emitted ESM output under real Node.
package.json	Updates build script to run tsc (but currently has an eval bug).
package-lock.json	Removes tsup and its dependency tree from the lockfile.
.github/copilot-instructions.md	Updates contributor instructions to reflect the new build.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 7 changed files in this pull request and generated no new comments.