fix(api): treat empty optional env vars as unset

[stringbitking]

Fixes #158 — a fresh clone's pnpm dev crashes the API and worker because .env.example ships the VERCEL_* keys as blank assignments (KEY=), dotenv delivers those as empty strings, and the min(1).optional() declarations in services/api/src/config.ts reject empty-present values.

What this does

Implements Option A from the issue: extends the blank-to-undefined preprocess idiom the file already uses for OptionalUrl, OptionalGithubOrganization, and FACILITY_PREVIEW_SURFACE_TOKEN to the whole optional non-empty group — VERCEL_TOKEN, VERCEL_OIDC_TOKEN, VERCEL_TEAM_ID, VERCEL_PROJECT_ID, FACILITY_AWS_CODEBUILD_PROJECT, FACILITY_AWS_CODEBUILD_CACHE_BASE_LOCATION, and PACKAGE_REGISTRY_TOKEN.

A blank or whitespace-only value now parses as unset (matching how facility doctor already reasons about these values via truthiness), while a value that is actually set must still be non-empty after trimming. Existing generated .env files heal without edits.

Why this doesn't change an intentional guarantee

• There is no cross-field validation requiring the tokens when FACILITY_SANDBOX_DRIVER=vercel — absent tokens already boot fine today, so the current min(1) only rejected one spelling of "not configured" while accepting the other.
• No existing test pinned the empty-string rejection; the Vercel config test covers trimming and OIDC-over-token precedence, both preserved.
• facility doctor remains the fail-fast surface for "driver selected but not configured".

Happy to rework toward Option B (comment the blank lines out of .env.example, keep the strict schema) if you prefer strict-presence semantics.

Tests

Two new cases in services/api/test/config.test.ts:

• the exact .env-template shape (all seven keys blank) boots and resolves every value to undefined;
• a whitespace-only value resolves identically to the key being absent.

vitest run test/config.test.ts: 16 passed. tsc --noEmit and biome check clean on the touched files.

🤖 Generated with Claude Code