fix: prebuild coderd before Playwright startup for e2e tests (#27136)

The test-e2e job could flake while Playwright waited for its webServer
to become ready. CI already built site/e2e/bin/coder, but that binary
was built before pnpm build and without the embed tag, so Playwright
ignored it and started coderd with go run -tags embed instead. That put
Go compilation, including frontend asset embedding, inside Playwright's
webServer timeout.

Local runs had a similar ordering trap. pnpm playwright:test invoked
Playwright directly, and Playwright starts webServer before globalSetup,
so the existing preflight build could not guarantee a binary existed
before webServer startup.

Build the E2E coder binary with the embed tag and make it depend on
site/out/index.html. In CI, build the frontend first, then build the E2E
binary, then run Playwright. For local runs, have pnpm playwright:test
and pnpm playwright:test-ui run make site/e2e/bin/coder before invoking
Playwright.

Playwright now starts the prebuilt site/e2e/bin/coder binary and waits
on the public /healthz endpoint instead of an authenticated API
endpoint. This keeps compilation outside the webServer readiness timeout
and makes the readiness probe quieter and more direct. I moved to
/healtz because the existing endpoint was returning 401, which still
means “server is up,” but it is a strange readiness signal. /healthz is
explicitly public and returns 200 OK once the HTTP server is accepting
requests.

Caveat: running pnpm exec playwright test
--config=e2e/playwright.config.ts directly bypasses the package script
and therefore bypasses the prebuild. Use pnpm playwright:test or make
test-e2e for the supported local flow.

Because the site package scripts now call make, add make to knip's
ignored
system binaries.

Tests:
- pnpm lint:types
- pnpm exec playwright test --config=e2e/playwright.config.ts --list
-
PATH="/opt/homebrew/opt/make/libexec/gnubin:/opt/homebrew/opt/gnu-getopt/bin:$PATH"
make gen/mark-fresh
-
PATH="/opt/homebrew/opt/make/libexec/gnubin:/opt/homebrew/opt/gnu-getopt/bin:$PATH"
pnpm playwright:test --list

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Makefile

@@ -1690,9 +1690,9 @@ test-clean:
 	go clean -testcache
 .PHONY: test-clean
 
-site/e2e/bin/coder: go.mod go.sum $(GO_SRC_FILES)
+site/e2e/bin/coder: go.mod go.sum $(GO_SRC_FILES) site/out/index.html
 	go build -o $@ \
-		-tags ts_omit_aws,ts_omit_bird,ts_omit_tap,ts_omit_kube \
+		-tags embed,ts_omit_aws,ts_omit_bird,ts_omit_tap,ts_omit_kube \
 		./enterprise/cmd/coder
 
 test-e2e: site/e2e/bin/coder site/node_modules/.installed site/out/index.html