feat(intent): posts: declarative event-driven row posting (stage 1 - model + glue)

[delchev]

What

First stage of posts: - a declarative construct that, on a document event, emits mapped rows
into a target entity (per line item), idempotently by a back-reference. It replaces the recurring
hand-written ledger/journal-posting glue (e.g. goods documents → StockMovement lines; document →
GL journal line) - ~8 hand-written delegates/listeners in one KeyFolders module alone.

This PR lands the model + structural glue + test only; the handler template and BPMN/listener
wiring are the next stages (kept small for review).

Changes

• PostIntent model: name, forEntity, event, forEach, into, idempotentBy, guard,
  set (field → value).
• IntentModel.posts + accessors.
• GlueIntentGenerator.buildPosts - emits the glue descriptor per rule: source entity, trigger
  event, per-item collection, target, idempotency back-reference, and the pascal-cased field map
  (Calc values - constants, Master.field, item.field, sign-flip expressions - pass through
  verbatim).
• GluePostsTest - asserts the emission for a goods-issue-ledger example.

Authoring shape

posts:
  - name: goodsIssueLedger
    forEntity: GoodsIssue
    event: POSTED            # a document status value, or `create`
    forEach: items           # composition-child collection (omit = one row per master)
    into: StockMovement       # target entity (local or cross-model)
    idempotentBy: GoodsIssue  # back-reference FK; skip if target rows already exist
    guard: negativeStock      # optional precondition
    set:
      Product:  item.Product
      Quantity: "-item.Quantity"   # sign flip via Calc expression
      GoodsIssue: Issue.Id         # the back-reference

Note the trigger key is event:, not on: - on is a YAML 1.1 boolean keyword (SnakeYAML
resolves the key to a boolean, so an on: field never binds).

Verification

engine-intent 217/217 green (incl. the new GluePostsTest).

Follow-ups (separate PRs)

• Handler template: an idempotent status-delegate (event = a status value) / create-listener
  (event = create) that renders set: through the Calc engine and does the idempotentBy
  pre-check; wire it to the trigger (BPMN apply step / -transitioned topic / create topic).
• Emission oracle; then adopt in the inventory module (retire the 6-7 ledger delegates) and verify
  the ledger posts identically.

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