Add host registration, heartbeat, and multi-host management

Implements the full host ↔ control plane connection flow:

- Host CRUD endpoints (POST/GET/DELETE /v1/hosts) with role-based access:
  regular hosts admin-only, BYOC hosts for admins and team owners
- One-time registration token flow: admin creates host → gets token (1hr TTL
  in Redis + Postgres audit trail) → host agent registers with specs → gets
  long-lived JWT (1yr)
- Host agent registration client with automatic spec detection (arch, CPU,
  memory, disk) and token persistence to disk
- Periodic heartbeat (30s) via POST /v1/hosts/{id}/heartbeat with X-Host-Token
  auth and host ID cross-check
- Token regeneration endpoint (POST /v1/hosts/{id}/token) for retry after
  failed registration
- Tag management (add/remove/list) with team-scoped access control
- Host JWT with typ:"host" claim, cross-use prevention in both VerifyJWT and
  VerifyHostJWT
- requireHostToken middleware for host agent authentication
- DB-level race protection: RegisterHost uses AND status='pending' with
  rows-affected check; Redis GetDel for atomic token consume
- Migration for future mTLS support (cert_fingerprint, mtls_enabled columns)
- Host agent flags: --register (one-time token), --address (required ip:port)
- serviceErrToHTTP extended with "forbidden" → 403 mapping
- OpenAPI spec, .env.example, and README updated

db/migrations/20260316223629_host_mtls.sql

@@ -0,0 +1,11 @@
+-- +goose Up
+
+ALTER TABLE hosts
+    ADD COLUMN cert_fingerprint TEXT,
+    ADD COLUMN mtls_enabled     BOOLEAN NOT NULL DEFAULT FALSE;
+
+-- +goose Down
+
+ALTER TABLE hosts
+    DROP COLUMN cert_fingerprint,
+    DROP COLUMN mtls_enabled;

db/queries/hosts.sql

@@ -13,12 +13,12 @@ SELECT * FROM hosts ORDER BY created_at DESC;
 SELECT * FROM hosts WHERE type = $1 ORDER BY created_at DESC;
 
 -- name: ListHostsByTeam :many
-SELECT * FROM hosts WHERE team_id = $1 ORDER BY created_at DESC;
+SELECT * FROM hosts WHERE team_id = $1 AND type = 'byoc' ORDER BY created_at DESC;
 
 -- name: ListHostsByStatus :many
 SELECT * FROM hosts WHERE status = $1 ORDER BY created_at DESC;
 
--- name: RegisterHost :exec
+-- name: RegisterHost :execrows
 UPDATE hosts
 SET arch = $2,
     cpu_cores = $3,
@@ -28,7 +28,7 @@ SET arch = $2,
     status = 'online',
     last_heartbeat_at = NOW(),
     updated_at = NOW()
-WHERE id = $1;
+WHERE id = $1 AND status = 'pending';
 
 -- name: UpdateHostStatus :exec
 UPDATE hosts SET status = $2, updated_at = NOW() WHERE id = $1;
@@ -64,3 +64,6 @@ UPDATE host_tokens SET used_at = NOW() WHERE id = $1;
 
 -- name: GetHostTokensByHost :many
 SELECT * FROM host_tokens WHERE host_id = $1 ORDER BY created_at DESC;
+
+-- name: GetHostByTeam :one
+SELECT * FROM hosts WHERE id = $1 AND team_id = $2;

db/queries/teams.sql

@@ -21,3 +21,6 @@ UPDATE teams SET is_byoc = $2 WHERE id = $1;
 
 -- name: GetBYOCTeams :many
 SELECT * FROM teams WHERE is_byoc = TRUE ORDER BY created_at;
+
+-- name: GetTeamMembership :one
+SELECT * FROM users_teams WHERE user_id = $1 AND team_id = $2;