fix(build): copy schema.json to dist and externalize zod

[ochafik]

Summary

Two focused packaging fixes in build.bun.ts.

Bug 1: ./schema.json export was broken

package.json exports "./schema.json": "./dist/src/generated/schema.json" but nothing copied the file there — tsc is emitDeclarationOnly and Bun.build doesn't emit JSON assets. Consumers importing @modelcontextprotocol/ext-apps/schema.json got ERR_MODULE_NOT_FOUND.

Fix: cpSync the file after tsc runs.

Bug 2: zod bundled despite being a peerDependency

zod is declared as a peer in package.json but was absent from every external list in build.bun.ts, so it was bundled into every entry point. This causes dual-instance bugs: consumer-side instanceof ZodError checks and schema.extend() calls break when operating across two separate zod runtimes.

Fix: Add zod to the external list for all non-*-with-deps entries. app-with-deps intentionally bundles everything and is left unchanged.

Bundle size impact

Entry	Before	After	Δ
app.js	293,952	24,561	−91.6%
app-bridge.js	299,517	30,112	−89.9%
react/index.js	295,558	26,153	−91.2%
server/index.js	291,500	22,135	−92.4%
app-with-deps.js	321,814	321,814	unchanged

Total shipped JS: ~1.50 MB → ~0.42 MB

Verification

# schema.json now present
$ ls dist/src/generated/schema.json
-rw-r--r--  216501  dist/src/generated/schema.json

# zod now external (import, not bundled)
$ rg -o 'ZodError|ZodType' dist/src/app.js | wc -l
0
$ rg -o 'from"zod"' dist/src/app.js | wc -l
1

# bundles load
$ node -e 'import("./dist/src/app.js").then(m => console.log(Object.keys(m).length))'
# → 38 exports

# unit tests pass
$ npm test
# → 87 pass, 0 fail

[pkg-pr-new]

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commit: e9aaf1e