Add agent onboarding tokens with Usage-page issuance UI

Per-node onboarding tokens replace the placeholder <token> in the agent
connect command: raw cagt_ tokens are returned once at issuance, only
sha256 hashes persist in agent_auth_tokens, and listing exposes metadata
only. Public agent routes accept env-configured shared tokens or any
active DB-issued token; successful validation stamps last_used_at and
revoked tokens are rejected — verified end-to-end against a real stack
(register, heartbeat, revoke → 401, bogus → 401).

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/internal/database/sqlcdb/agent_tokens.sql.go

@@ -0,0 +1,122 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.31.1
+// source: agent_tokens.sql
+
+package sqlcdb
+
+import (
+	"context"
+
+	"github.com/google/uuid"
+)
+
+const createAgentAuthToken = `-- name: CreateAgentAuthToken :one
+INSERT INTO agent_auth_tokens (token_hash, label)
+VALUES ($1, $2)
+RETURNING id, token_hash, label, created_at, last_used_at, revoked_at
+`
+
+type CreateAgentAuthTokenParams struct {
+	TokenHash string `json:"token_hash"`
+	Label     string `json:"label"`
+}
+
+func (q *Queries) CreateAgentAuthToken(ctx context.Context, arg CreateAgentAuthTokenParams) (AgentAuthToken, error) {
+	row := q.db.QueryRowContext(ctx, createAgentAuthToken, arg.TokenHash, arg.Label)
+	var i AgentAuthToken
+	err := row.Scan(
+		&i.ID,
+		&i.TokenHash,
+		&i.Label,
+		&i.CreatedAt,
+		&i.LastUsedAt,
+		&i.RevokedAt,
+	)
+	return i, err
+}
+
+const getActiveAgentAuthTokenByHash = `-- name: GetActiveAgentAuthTokenByHash :one
+SELECT id, token_hash, label, created_at, last_used_at, revoked_at FROM agent_auth_tokens
+WHERE token_hash = $1 AND revoked_at IS NULL
+LIMIT 1
+`
+
+func (q *Queries) GetActiveAgentAuthTokenByHash(ctx context.Context, tokenHash string) (AgentAuthToken, error) {
+	row := q.db.QueryRowContext(ctx, getActiveAgentAuthTokenByHash, tokenHash)
+	var i AgentAuthToken
+	err := row.Scan(
+		&i.ID,
+		&i.TokenHash,
+		&i.Label,
+		&i.CreatedAt,
+		&i.LastUsedAt,
+		&i.RevokedAt,
+	)
+	return i, err
+}
+
+const listAgentAuthTokens = `-- name: ListAgentAuthTokens :many
+SELECT id, token_hash, label, created_at, last_used_at, revoked_at FROM agent_auth_tokens
+ORDER BY created_at DESC
+`
+
+func (q *Queries) ListAgentAuthTokens(ctx context.Context) ([]AgentAuthToken, error) {
+	rows, err := q.db.QueryContext(ctx, listAgentAuthTokens)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	items := []AgentAuthToken{}
+	for rows.Next() {
+		var i AgentAuthToken
+		if err := rows.Scan(
+			&i.ID,
+			&i.TokenHash,
+			&i.Label,
+			&i.CreatedAt,
+			&i.LastUsedAt,
+			&i.RevokedAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Close(); err != nil {
+		return nil, err
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const revokeAgentAuthToken = `-- name: RevokeAgentAuthToken :one
+UPDATE agent_auth_tokens SET revoked_at = NOW()
+WHERE id = $1 AND revoked_at IS NULL
+RETURNING id, token_hash, label, created_at, last_used_at, revoked_at
+`
+
+func (q *Queries) RevokeAgentAuthToken(ctx context.Context, id uuid.UUID) (AgentAuthToken, error) {
+	row := q.db.QueryRowContext(ctx, revokeAgentAuthToken, id)
+	var i AgentAuthToken
+	err := row.Scan(
+		&i.ID,
+		&i.TokenHash,
+		&i.Label,
+		&i.CreatedAt,
+		&i.LastUsedAt,
+		&i.RevokedAt,
+	)
+	return i, err
+}
+
+const touchAgentAuthToken = `-- name: TouchAgentAuthToken :exec
+UPDATE agent_auth_tokens SET last_used_at = NOW()
+WHERE token_hash = $1 AND revoked_at IS NULL
+`
+
+func (q *Queries) TouchAgentAuthToken(ctx context.Context, tokenHash string) error {
+	_, err := q.db.ExecContext(ctx, touchAgentAuthToken, tokenHash)
+	return err
+}