fix(kyberforge): fix apm-scope validation gaps in agent/skill authoring scripts

Post-implementation review of PR #93 (issue #89's apm.yml-native retargeting
of skill-author/skill-audit/agent-author/agent-audit) found four confirmed
defects across the four scripts' apm.yml `type:` walk-up logic:

- field-inventory.md's apm-agent-allowlist was missing `source_keys`,
  contradicting agent-author/SKILL.md's own instruction (Step 5 checklist)
  to allow it at plugin/APM scope — a correctly-authored file with
  source_keys failed validate.sh.
- validate.sh's APM_TYPE_RE and validate-provenance.sh's TYPE_RE disagreed:
  the former tolerated a quoted `type: "skill"` value, the latter didn't,
  despite agent-audit/SKILL.md explicitly documenting that
  validate-provenance.sh walks up "the same way validate.sh does". Both
  also used `\b` word-boundary matching, which false-matches a malformed
  value like `type: prompts-only` on the `prompts` prefix. Unified both
  regexes to be quote-tolerant and require an exact value.
- All four scripts' `.git` project-boundary check used isdir()/[[ -d ]],
  which misses git worktrees where `.git` is a regular file (`gitdir: ...`)
  rather than a directory. Switched to exists()/[[ -e ]].
- new-agent.sh and new-skill.sh had the same quote-intolerance as above via
  inline `grep -qE` calls (new-skill.sh's also had the `\b` false-match
  bug); replaced both with a shared-shape `is_apm_package_manifest` bash
  helper matching the Python regex's semantics.

Four other findings from the same review turned out not to be bugs: a
bare `plugin.json` no longer signaling plugin scope is documented,
intentional behavior (agent-audit/SKILL.md:30, agent-author/SKILL.md:87),
deferred to issue #90's real plugin.json-to-apm.yml conversion — not
something this fix should reverse.

Verified via direct reproduction of each defect plus the full test suite:
147/147 bats tests, 39/39 shell-script tests, 12/12 summary categories.

Refs: #89

plugins/kyberforge/skills/agent-audit/scripts/validate-provenance.sh

@@ -54,7 +54,12 @@ if not (fname.endswith('.agent.md') or fname.endswith('.md')):
     print(f"Error: unrecognized extension '{fname}' — expected .md or .agent.md", file=sys.stderr)
     sys.exit(2)
 
-TYPE_RE = re.compile(r'^type:\s*(instructions|skill|hybrid|prompts)\b')
+# Matches a top-level `type:` line whose value is exactly one of the four
+# package content types — identical to validate.sh's APM_TYPE_RE. Group 1's
+# optional quote must be closed by \1 (or nothing), and the value must be
+# followed by whitespace/end-of-line so a malformed value like `prompts-only`
+# doesn't false-match on the `prompts` prefix.
+TYPE_RE = re.compile(r"^type:\s*(['\"]?)(instructions|skill|hybrid|prompts)\1(?:\s|$)")
 
 # --- Find package root: walk up for the nearest ancestor apm.yml that
 # declares a top-level type: field. An apm.yml with no type: field is a
@@ -69,7 +74,9 @@ def find_plugin_root(start_dir):
             with open(apm_yml) as f:
                 if any(TYPE_RE.match(line) for line in f):
                     return current
-        if os.path.isdir(os.path.join(current, '.git')):
+        # .git is a directory in a normal checkout but a file (`gitdir: ...`)
+        # in a git worktree — exists() covers both.
+        if os.path.exists(os.path.join(current, '.git')):
             return None
         parent = os.path.dirname(current)
         if parent == current: