Control plane: projects.owner → org_id + admin API + migration

[axelgar]

What to build

Re-scope projects from a single user to an org. Today projects.owner is a user id; it becomes org_id, and every "my projects" path re-scopes to "this org's projects". Includes a one-time migration so existing single-owner projects don't get orphaned.

• Schema: projects.owner → org_id (services/counter/src/schema.ts).
• Control plane (db.ts): createProject and listProjects(owner) → listProjects(orgId); admin GET /v1/projects?owner= → ?org=. The counter only needs org_id for billing attribution — member/role authz stays in the dashboard, which holds the better-auth session.
• Dashboard queries pass the active org_id to the counter admin API (requireUser() / lib/session.ts gains an active-org notion).
• Migration: one-time, idempotent (Neon-http has no transactions) — for each existing project, ensure a personal org for the current owner, set org_id, run once, verify counts.

Acceptance criteria

• projects keys off org_id; listProjects / admin API scope by org.
• Dashboard "my projects" shows the active org's projects.
• Existing projects migrated into personal orgs with no data loss; usage unaffected.
• Migration is idempotent and verified by count.

Blocked by

• better-auth org plugin + schema + auto-personal-org on signup #10 (needs orgs to exist)