Borg: a happy path and easy tests for any framework (umbrella) #2326

Borg assimilates all: almost any framework gets a happy path through Rusty Buns that is already worked out, and every one of them can be tested easily. This issue stacks the framework concerns that stand between us and that. One child per concern. They started as note files in PRs #2270 and #2234 (closed) and #2250 (still open for its CI change).

• Frameworks: how Wasp, RWSDK and Elysia fit beside Rusty Buns #2327 Frameworks: how Wasp, RWSDK and Elysia fit beside Rusty Buns (which get a happy path, which don't)
• Make even more use of Alchemy #2328 Make even more use of Alchemy (deploy, previews and the test harness are what make a framework easy to test; already split out: Bump Alchemy to 2.0.0-beta.84 (package split) and turn off its telemetry #2235, Shared Alchemy state: postgresState on Neon instead of the git-dir symlink #2237, Preview deploy on demand (Worker Previews + PR comment, destroyed on close) #2238)
• Faster test loop: rented box and local build monster #2329 Faster test loop: rented box and local build monster (trying many frameworks quickly)
• MANUAL RUN: set up the Macs as test builders (Docker limits, images, timings) #2330 MANUAL RUN: set up the Macs as test builders

Related: #318 (framework support), #1526 (Borg Mervin, the merge side).

Existing Borg work to keep in line with this: apps/borg-postgres, .github/workflows/borg-edge.yml, and the closed slim/thick/fatty borg issues #855, #856, #857.