docs: clarify memory lifecycle across flows

[mason5052]

Summary

• document how PentAGI memory behaves across flows
• clarify the difference between flow-scoped execution memory and reusable vector documents
• add practical guidance for storing reusable target knowledge between engagements

Problem

Issue #74 asks whether PentAGI should keep memory after flows are removed and how users should preserve target knowledge between runs. The current repository already has the underlying concepts (memory, guide, answer, code, Graphiti, and flow_id filters), but the docs do not explain how they fit together operationally.

Solution

• add a new "Memory Lifecycle Across Flows" section to the README near the embedding and etester documentation
• explain when to inspect vector documents with flow_id and when to store durable knowledge explicitly as guide, answer, or code
• extend backend/docs/flow_execution.md with lifecycle guidance that distinguishes flow-scoped execution history from reusable knowledge and references the current prompt-template behavior

User Impact

Users now have a clearer path for deciding what should stay attached to a single engagement and what should be stored intentionally for future flows. This makes it easier to preserve reusable target notes without assuming that raw execution history alone will provide the right cross-run context.

Test Plan

• verify the new README guidance matches the current etester search options and embedding docs
• verify the lifecycle notes match the documented vector store types and prompt-template memory model
• run git diff --check

Closes #74

[Copilot]

Pull request overview

Adds documentation clarifying how PentAGI’s memory/knowledge storage behaves across flows, and how to persist reusable context between engagements (issue #74).

Changes:

• Add “Memory Lifecycle Across Flows” guidance to the README near the etester embedding/search documentation.
• Extend backend/docs/flow_execution.md with lifecycle guidance distinguishing flow-scoped execution history (memory) from reusable knowledge (guide/answer/code).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
backend/docs/flow_execution.md	Adds lifecycle guidance on when to rely on flow-scoped memory vs storing durable guide/answer/code.
README.md	Adds a new section explaining practical workflows for inspecting per-flow history and persisting reusable target knowledge.

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