IAV-1250/fix(public-tender): Slack webhook merge + platform UID headers
- Add AddPlatformIntegrationResponse.webhookUrl; persist extracted Slack webhook URL on the agent when adding Slack integration.
- PublicMarketIntegrationServiceImpl: resolve Slack webhook id from deployed workflow or default public-tender-agent-{ownerUid}; replace workflow template placeholders (Slack, agent, user, API base, OpenAI) when merging platform nodes; pass agentUid through merge; extract URL from slackTrigger/webhook nodes.
- JwtSecurityUtils: resolve IAVIA platform user from X-User-UUID / X-USER-UID with optional JWT validation when resource server is configured; document local vs production.
- SecurityConfig: clarify OAuth2 resource server / JwtDecoder requirement.
- PublicMarketWizardServiceImpl: warn log on replicateIntegration when caller UID != agent owner.