Feature: Fix documentation gaps — incorrect references, missing parameters, outdated attributes

[FernandoCelmer]

Idea

Fix documentation gaps found during code review: incorrect member references, missing parameter docs, outdated attribute names.

Critical — Incorrect docs

• docs/nav/reference/context.md: Lists result_task, result_context, result_storage that don't exist in Context class
• docs/nav/reference/config.md: Lists path, task_path, log_path, output that don't exist in Config class
• docs/nav/reference/task-instance.md: Lists _error but attribute is now _errors
• dotflow/core/action.py:75: Docstring says backoff (int) but type is bool
• dotflow/core/config.py:40: Docstring says log: Type of the **notify** — copy-paste error

High — Undocumented features

• DotFlow(workflow_id=...) not documented in docstring or reference
• Manager(resume=True) not in reference page
• task.errors / task.retry_count not in reference
• task.error deprecation not in reference
• DotFlow.result() not listed in reference
• TaskBuilder.schema() / result() not in reference

Medium — Tutorial gaps

• Checkpoint + group_name interaction not explained
• Backoff algorithm not explained (doubles delay each retry)