feat(reflow): add in-memory history tracking for Flow edits

[abdelaziz-mahdy]

Problem

Reflow flows have no visible change history. Once a flow is saved, prior versions and property-level diffs are lost from the UI — reviewers can't see who edited a flow, when, or what fields changed.

Solution

Wrap HistoryDAO inside the flow journal so JDAO replay passes each persisted put through history on startup. Store history records in an in-memory MDAO keyed by a SequenceNumberDAO so the composite id (objectId, seqNo) stays unique across multiple edits of the same flow. Expose the history per flow via a transient DAOProperty and render it with a new FlowHistoryView.

Because history lives in memory, it rebuilds from the flows journal on every boot — no separate history journal, no unbounded growth. Live edits after boot append normally.

Changes

• services.jrl — add flowHistoryDAO CSpec (in-memory MDAO wrapped in SequenceNumberDAO); rewire flowDAO to construct HistoryDAO(flowHistoryDAO, new MDAO(Flow)) and pass it to EasyDAO.setMdao(...) so JDAO wraps around history rather than around the bare MDAO.
• Flow.js — add foam.mlang.Expressions to implements, import flowHistoryDAO?, add a historySection and a transient history DAOProperty that filters flowHistoryDAO by objectId and orders by seqNo desc.
• FlowHistoryView.js — new view rendering each history record as a collapsible row: timestamp, user, summary of changed property names, and an expandable diff grid showing property | old | new with semantic colour tokens. Mixes in foam.u2.util.ClipboardAccess and adds a hover copy button per value cell.
• pom.js — register FlowHistoryView.