Port Bun Bake production builds to home build --app

Scope

Routing home build through the native Bun-compatible BuildCommand exposes the upstream --app production-build branch. Home has the Bake types and development-server substrate, but bake.production.buildCommand is not ported yet, so the CLI now reports this gap explicitly instead of hiding it behind the old outer build dispatcher.

Acceptance criteria

• Port Bun's production Bake build command against Home's native runtime.
• Support the dynamic and static production modes and their client/server build graphs.
• Preserve the upstream import.meta.env.DEV, PROD, MODE, SSR, and STATIC defines.
• Add focused tests for home build --app output and failure diagnostics.
• Remove the temporary BakeProductionBuildNotImplemented boundary once production builds run.

Parent: #66 Discovered while completing: #550

Completed in 5d560ae27a2a189b48f47723a3628a1e02067921 (feat(runtime): enable Bake production builds).

What landed:

• replaced Home's BakeProductionBuildNotImplemented boundary with the pinned Bun runtime/bake/production.zig pipeline;
• ported the full Bake framework/config parser from Bun 4982b91e3702094330f3be3883354c52b8c01323, including split client/server/SSR bundler options, router styles, built-in modules, server-components settings, and production/development mode defines;
• embedded Bun's four bun-framework-react sources;
• connected the real framework virtual modules, route graph, client/server bundlers, server module loading, prerender callbacks, and output writer;
• fixed the client-transpiler optional payload initialization that trapped in the Bake browser graph;
• normalized absolute chunk destinations into dist/_bun and reject parent traversal, so client output cannot escape the production output directory;
• allowed valid custom frameworks whose bundle has no shared runtime chunk;
• added an end-to-end test-bake-production build step.

The integration fixture proves:

• a static / route renders to dist/index.html;
• a dynamic [slug] route expands through getParams() into /alpha and /beta output;
• client assets are emitted under dist/_bun with no sibling _bun escape;
• import.meta.env.DEV, PROD, MODE, SSR, and STATIC evaluate to the pinned Bun production-static values;
• a missing --app config exits nonzero with the expected resolution diagnostic.

The pinned Bun production command itself selects production_static; the shared port also carries production_dynamic mode/config semantics. Live dynamic serving and HMR are tracked separately in #553.

Verification:

• zig build test-bake-production -Denable_jsc=true -j1 ...: 18/18 steps succeeded
• scoped native runtime suite: 1,822 passed, 19 skipped, 0 failed (20/20 build steps)
• zig build debug -Denable_jsc=false -j1 ...: 5/5 steps succeeded
• scoped Pickier check: clean
• git diff --check: clean