docs: lifecycle stages, report scope, and status references by name

[delchev]

Renders the specification change proposed in IntentFile/intent-specification#6 (implemented in the reference implementation as eclipse-dirigible/dirigible#6647, for eclipse-dirigible/dirigible#6645).

Why: an aggregation over an entity that carries a lifecycle is wrong by default — drafts nobody has issued, cancelled and voided documents all land in the sum unless the author remembers a predicate over positional status ids, and nothing in the format said so. The addition declares a status's meaning once, where the nomenclature is seeded, and lets reports and guards resolve it.

What changed

• spec/data — a stage section under seeds: the draft | live | cancelled | void vocabulary as a table, why the meaning belongs with the nomenclature rather than being re-derived in every predicate, and the normative rules (metadata never becomes a column; a classified row carries its primary key; a colliding stage property is reported, not guessed at). Plus Status references — name, not number, covering every site that names a status, with the positional-id argument spelled out.
• spec/presentation — a Lifecycle scope section under reports: the three shapes (implicit live, scope: all, an explicit stage), and the normative rules for when the implicit default applies, the two conditions that stand it down (a status dimension, an authored status filter), and the diagnostic a conforming generator must report when nothing is resolvable.
• reference — a scope row; the reports, transitions and seeds snippets updated to show scope:, symbolic statuses and stage:; the cross-model boundary added under Planned.

Left open for maintainer review — the specification PR governs the wording, and this only renders it. vitepress build is clean and the three new anchors resolve (#lifecycle-scope, #stage-what-a-status-means-to-the-lifecycle, #status-references-name-not-number).