[codex] Replace stale project plan with implementation docs

[samlaycock]

Summary

Closes #189.

This removes the stale PROJECT.md planning document and replaces it with focused implementation docs under docs/ for future contributors.

The new docs cover:

• app registration, route discovery, layouts, manifests, and matching
• route loaders/actions, resources, API routes, input parsing, and middleware
• view(...) responses, React Server Components, Flight transport, and client/server boundaries
• Vite plugin responsibilities, virtual modules, dev middleware, HMR, and production build output
• runtime dispatch, deployment model, result helpers, headers, revalidation, and error handling

Why

PROJECT.md described older v1 planning scope and removed configuration/API concepts. Keeping it as a single large plan made it easy for contributor guidance to drift from the current public API and implementation.

Validation

• bun test tests/implementation-docs.test.ts tests/docs-package-names.test.ts
• bun fmt
• bun lint:fix
• bun test
• bun typecheck
• bun run build

Changeset

Included .changeset/quiet-cameras-reflect.md documenting the docs replacement.

[greptile-apps]

Greptile Summary

This PR replaces the stale PROJECT.md planning document (1,493 lines) with five focused implementation reference docs under docs/, covering app registration, server handlers, RSC/Flight transport, the Vite build pipeline, and runtime/deployment behaviour.

• The new docs address both open review threads from the previous round: server-handlers.md now explicitly states that component is required on resources and that middleware does not receive parsed input.
• The previously duplicated readDoc helper is extracted to tests/helpers/read-doc.ts and consumed by both tests/docs-package-names.test.ts and the new tests/implementation-docs.test.ts, which guards against PROJECT.md re-appearing and against removed API names leaking back into the docs.

Confidence Score: 5/5

Pure documentation and test change with no production code modifications — safe to merge.

All changed files are Markdown docs, test helpers, and test suites. No runtime or library code is touched. The new tests actively prevent both regression to removed APIs and re-introduction of the stale plan, and both previously open review threads are now resolved in the docs themselves.

No files require special attention.

Important Files Changed

Filename	Overview
docs/server-handlers.md	New doc covering route loaders/actions, resources (with explicit note that component is required), API routes, input parsers, and middleware — addresses both issues flagged in the previous review round
docs/app-and-route-discovery.md	New doc covering explicit app registration, routes/layouts, filesystem discovery globs, manifests, and matching
docs/runtime-deployment-and-errors.md	New doc covering request dispatch order, internal request validation hook, result helpers, redirect/invalid defaults, and error vs fault handling
tests/helpers/read-doc.ts	New shared helper that extracts the readDoc utility previously duplicated across test files
tests/implementation-docs.test.ts	New test suite that asserts PROJECT.md is gone, all new docs exist, key API names are present, and removed APIs are not re-introduced
tests/docs-package-names.test.ts	Updated to import readDoc from the shared helper and to check the new implementation docs instead of the deleted PROJECT.md

_{Reviews (2): Last reviewed commit: "docs: address implementation review feed..." | Re-trigger Greptile}