Generalize workflows for document-free automation

[paullizer]

Summary

• Replace the single-pane workflow form with a five-step General, Trigger, Tasks, Reliability, and Review builder for personal and group workflows.
• Add ordered instruction tasks that share the selected model or agent and receive bounded prior-task output context.
• Add per-task retries and halt-or-continue error handling, task run items, and task lifecycle events in workflow activity.
• Keep File Sync and document Search, Analyze, or Compare as optional inputs; document input applies to task one and later tasks consume its result.
• Preserve workflows without a tasks array on the legacy single-dispatch path.

Validation

• 12/12 focused functional checks passed across stepped UI, task runtime, generic workflow compatibility, and Direct Model capabilities.
• JavaScript and Python syntax checks, editor diagnostics, and git diff --check passed.
• Revision-scoped XSS and broken access control guardrails passed.
• Azure Playwright module is updated and discoverable, but skipped locally because authenticated SIMPLECHAT_UI_BASE_URL/storage state was unavailable; the fresh local server redirects to Microsoft sign-in.

Fixes #1082