refactor(nx2/api): unify return shapes, rename methods, add response helpers

[chrischrischris]

Consolidates the nx2 api surface around a single rule — every namespace method
returns a raw augmented Response — and aligns method/arg naming across
namespaces.

Renames (call sites updated):

• source.load -> source.get
• source.save({data}) -> source.save({body})
• config.put -> config.save
• snapshot.update -> snapshot.save (matches AEM's createSnapshot upsert)

Return-shape unification (raw Response everywhere except source.list):

• source.delete/copy/move: dropped wrapActionResp -> Response
• source.getMetadata: dropped {ok,status,headers} wrapper -> Response (caller
  reads resp.headers for doc-id, last-modified, etc.)
• status.get: dropped parsed-JSON / undefined return -> Response
• aem.*: dropped returnJson flag, dropped 204 wrapper on unPreview/unPublish,
  callPath returns Response directly.
• source.list is the documented exception: still returns {ok, items,
  continuationToken, permissions} because it legitimately merges body +
  header continuation token + normalized items.

New opt-in helpers (asJson, asText) — both return
{ ok, data, status, error } where data is the parsed body (populated even
on non-ok when parseable, matches axios), status is the HTTP code, and
error is null | 'no-response' | 'not-ok' | 'parse-failed'. No asOk —
const { ok } = await foo() does the same job.

Other fixes:

• snapshot.addPath/removePath auto-prepend / to path inputs (latent bug:
  callers passing 'index.html' would build .../{id}index.html). New
  normalizePath helper handles both string and array forms.

File layout reorganized so the public namespaces are at the top
(alphabetical), then response helpers, then low-level fetch primitives,
then internal helpers. Internal helpers converted from arrow-consts to
function declarations for hoisting.

Docs:

• api.d.ts: new UnwrapResult type; method signatures tightened to
  Promise with documented exceptions.
• api.md: rewrote return-values, error-handling, and aem/status sections;
  added helpers section.

Tests: 90/90 pass. Notable: chai.deep.equal against a Response hangs Chrome
(traverses the body ReadableStream); switched the affected assertions to
expect(resp.ok)/expect(resp.status).

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Commits

• 9252ae9 ✅ (latest)
• cf65db1 ✅
• 800112f ✅