fix(kyberforge): harden plugin-content sync, reinject Copilot mcpServers

PR #95's review of the issue #90 apm-conversion work found several
defects in scripts/sync-plugin-content.sh and the gate wired to it:

- --check claimed never to mutate the plugin root, but apm pack still
  wrote .claude-plugin/plugin.json and .github/plugin/plugin.json into
  the real plugin_dir on first-time creation. --check now packs a
  throwaway copy instead.
- check-plugin-content-sync hardcoded the six plugin directories
  instead of deriving them the way check-manifests.sh already does.
  Added an --all flag that parses .claude-plugin/marketplace.json, and
  simplified the pre-commit hook to use it.
- A missing plugin_dir and one that legitimately has no .apm/ yet both
  reported SKIP/success; a missing directory now FAILs.
- The dispatch loop backgrounded every plugin with no concurrency cap,
  unlike the JOBS-bounded pattern this same PR added to
  tests/run-bats.sh and tests/run-tests.sh. Added the same
  bash-3.2-safe getconf + batched-wait cap here for consistency.
- Per-plugin scratch/log/status files were keyed only by basename, with
  no collision guard across arguments; added a fail-fast check.
- sync_hooks_json()'s trailing-newline normalization was duplicated
  between its --check and write branches; factored into one helper.
- tests/test-sync-plugin-content.sh set two competing `trap ... EXIT`
  statements, so the first (cleaning up $FIXTURE) was silently
  replaced by the second and its tmp dir leaked every run. Adopted the
  track()/CLEANUP_DIRS pattern already used in
  tests/test-check-release-needed.sh.

Separately: apm's Copilot-ecosystem plugin.json builder unconditionally
strips mcpServers, citing (in its own docstring) that the field is out
of schema for Copilot -- a claim this repo's own researched Copilot
plugin schema docs contradict. reinject_mcp_servers() narrowly restores
it from the plugin's .mcp.json on real syncs only, regenerating
plugins/bin/.github/plugin/plugin.json (the only plugin that currently
declares any MCP servers). Documented as an amendment to ADR-0017,
since it's a deliberate, narrow exception to that ADR's rejection of
patching apm's compiled output -- apm's premise for stripping
skills/agents/commands/hooks pointers is still accurate; its premise
for stripping mcpServers is not.

All 12 assertions in tests/test-sync-plugin-content.sh pass
individually, plus 5 new regression tests added for this round; the
full bats and shell-script suites are green; shellcheck is clean.

Refs: #95
ADR: 0017

plugins/bin/.github/plugin/plugin.json

@@ -16,5 +16,15 @@
     "prototyping",
     "tdd",
     "research"
-  ]
+  ],
+  "mcpServers": {
+    "obsidian": {
+      "args": [
+        "@bitbonsai/mcpvault@latest",
+        "docs/"
+      ],
+      "command": "npx",
+      "type": "stdio"
+    }
+  }
 }