Re-scope author super-skill to feature level (al-feature-author)

Turn the object-granularity al-object-author super-skill into the
feature/PR-level al-feature-author - the true authoring counterpart of
al-code-review, which takes a whole PR. feature-spec in -> whole-PR
code-artifact out.

- microsoft/skills/author/al-feature-author.md (renamed from
  al-object-author.md): takes inputs [feature-spec]; decomposes it into a
  cross-referenced object graph, allocates a contiguous object-ID block,
  applies the mandatory affix, resolves cross-object references (API page
  SourceTable = authored master), fans each derived object-spec out to the
  worklisted leaves, rolls up their artifacts, reconciles the refs, and
  enumerates the objects no current leaf authors (List/Card pages,
  permission set, install codeunit) as open-questions. Worked example:
  a Membership feature -> 3 artifacts (master table + setup table from
  al-table-author, API page from al-api-page-author) rolling up to completed.
- skills/do.md (composition v1.1, STABLE-CONTRACT): add feature-spec to the
  standard inputs; extend Relevance so a super-skill's inputs need not equal
  its leaves' - it may derive the leaves' inputs by decomposing its own;
  generalize Action rollup to findings-report OR code-artifact. Review
  (findings) semantics read identically - behavior-preserving.
- .github/scripts/validate_frontmatter.py: add feature-spec to STANDARD_INPUTS.
  #67 R26 generalization unchanged.
- README.md, agent-consumption.md: author family's top-level skill is now
  al-feature-author.

The al-table-author leaf and the R26 generalization from #67 are unchanged.
Knowledge article count unchanged at 199.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/scripts/validate_frontmatter.py

@@ -45,7 +45,7 @@ ENTRY_SKILL_REQUIRED_KEYS = {"kind", "id", "version", "title"}
 
 STANDARD_INPUTS = {
     "pr-diff", "object-list", "file-path", "repository", "telemetry-query",
-    "object-spec",
+    "object-spec", "feature-spec",
 }
 ALLOWED_OUTPUTS = {"findings-report", "code-artifact"}
 VALID_SAMPLE_KINDS = {"good", "bad"}