fix(auth): self-hoster opt-out for session-cookie Secure flag (v1.5.1)

v1.5.1 patch. Fixes the silent login failure self-hosters hit on
plain-HTTP origins that aren't localhost — the bundled Docker image
runs NODE_ENV=production, so every cookie carried Secure, and modern
browsers drop those on http://10.x.x.x style origins. The session
cookie never made it back to the browser, /api/auth/me returned 401,
and the login page reloaded.

New SESSION_COOKIE_SECURE env var with three values:
- unset (default) — flag follows NODE_ENV === "production" (unchanged)
- "false" — never set (LAN / VPN / Tailscale-only opt-out)
- "true"  — always set (pnpm dev fronted by HTTPS)

Shared helper at src/lib/auth/secure-cookie.ts replaces four scattered
literals across session, codex device-start, and withings connect.
Six unit cases pin the decision matrix.

OpenAPI spec generator now reads info.version from package.json so
the drift gate stays meaningful instead of catching every release bump.

Default behaviour unchanged for HTTPS-fronted deployments.

docs/api/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.5.0
+  version: 1.5.1
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.