fix(kyberforge): bridge apm content to Claude Code's flat plugin discovery

Claude Code's (and Copilot's) native plugin installer has zero awareness of
.apm/ nesting -- it convention-scans only flat skills/, agents/, commands/,
hooks.json at each plugin's root. Confirmed via strings on the installed
claude binary and live installs of git@holocron/gitea@holocron/kyberforge@
holocron, all reporting Skills(0) Agents(0) Hooks(0) post ADR-0015's apm
conversion. Root cause (apm_cli/core/plugin_manifest.py): apm's plugin.json
compiler deliberately strips skills/agents/commands keys, assuming the host
already auto-discovers those convention directories -- it has no model of
.apm/ being host-visible at all. Separately, apm's own bundle exporter
(apm_cli/bundle/plugin_exporter.py, behind `apm pack --format plugin`)
implements the correct .apm/ -> flat mapping, but only ever targeted
build/<name>-<version>/, a path nothing in marketplace.json's source: points
at.

scripts/sync-plugin-content.sh wraps that bundle exporter and copies its
agents/, skills/, commands/, instructions/, extensions/, and merged
hooks.json back into each plugin's own root as a second tracked
compiled-output category -- same governance status as
.claude-plugin/plugin.json: generated from .apm/, never hand-edited. tests/
subdirectories are excluded from the mirror (dev fixtures, not host-visible
runtime content; several hardcode a relative repo-root walk-up sized for the
.apm/-nested depth, which breaks when duplicated one level shallower).
Applied for real across all 6 plugins and verified two ways: `claude plugin
validate --strict` passes on every real plugin directory, and a live
`claude --plugin-dir <path> -p "list skills/agents"` behavioral test
confirms content is now actually discovered.

Also, from the same issue #90 review round:
- scripts/check-manifests.sh pointed at each plugin's root-level plugin.json
  (checking skills/hooks/mcpServers/agents pointer fields) -- that file was a
  stale near-duplicate of .claude-plugin/plugin.json nothing else read or
  wrote, now deleted across all 6 plugins. check-manifests.sh is rewritten to
  validate .claude-plugin/plugin.json instead, and drops the pointer-field
  checks entirely (nothing to check -- those fields are correctly absent by
  design). Content-presence drift is now check-plugin-content-sync's job, a
  new pre-push hook wired in .pre-commit-config.yaml.

docs/adr/0017 records the root cause and decision in full, including two
rejected alternatives (patching plugin.json's path fields directly -- apm's
compiler strips them on every run; pointing marketplace.json at apm pack's
build/ output -- a version-suffixed non-source directory nothing can install
from without an extra build step). ADR-0015 and CONTEXT.md are updated to
point at it.

Refs: #90

plugins/kyberforge/skills/apm-install/SKILL.md

@@ -0,0 +1,55 @@
+---
+name: apm-install
+description: >
+  Use when the user wants to install the apm (Agent Package Manager) CLI
+  itself, pin or upgrade its version, set up an air-gapped/enterprise mirror
+  install, or install and manage an agent runtime that apm drives (Copilot
+  CLI, Codex, Gemini, generic llm) — "install apm", "set up apm", "pin apm to
+  a version", "apm runtime setup", "which runtime will apm run pick". Do not
+  use for authoring apm.yml, scaffolding a package/marketplace, compiling,
+  packing, publishing, or running apm audit — use apm-workflow for those.
+metadata:
+  category: apm
+  source_keys:
+    - context7-microsoft-apm
+---
+
+## Gotchas
+
+- apm does not execute agents itself — it only installs and manages the runtimes that do. "Install apm" and "install a runtime apm manages" are two separate steps; don't conflate them or skip the second when the user actually wants a working agent CLI, not just the package manager.
+- The air-gapped/enterprise mirror path needs `GITHUB_URL` and `VERSION` set together against a downloaded `install.sh` — it does not work through the piped one-liner form.
+- `pip install apm-cli` requires Python 3.10+; the quick-install script has no such prerequisite. Prefer the quick-install script unless the environment is pip-first.
+- On a Debian/externally-managed Python environment (PEP 668), `pip install apm-cli` fails immediately with `error: externally-managed-environment`. Fall back to `pipx install apm-cli` — same PyPI package, but pipx creates an isolated venv and correctly exposes the `apm` binary on `PATH`.
+- Installing the Copilot CLI runtime through `apm runtime setup copilot` requires Node.js v22+ and npm v10+ already present — apm does not install Node/npm for you.
+
+## Install apm
+
+Default:
+
+```bash
+curl -sSL https://aka.ms/apm-unix | sh
+```
+
+Escape hatches — combine as needed:
+- Pin a version: append `@vX.Y.Z` to the piped script's arguments, e.g. `curl -sSL https://aka.ms/apm-unix | sh -s -- @v1.2.3`.
+- Custom install directory: set `APM_INSTALL_DIR` on the piped script's command, e.g. `curl -sSL https://aka.ms/apm-unix | APM_INSTALL_DIR=$HOME/.local/bin sh`.
+- Air-gapped / GitHub Enterprise mirror: download `install.sh` first, then run it with `GITHUB_URL` and `VERSION` set, e.g. `GITHUB_URL=https://github.corp.com VERSION=v1.2.3 sh install.sh`.
+- pip (Python 3.10+ environments): `pip install apm-cli`.
+- pipx (externally-managed/PEP 668 environments where plain `pip install` fails, e.g. Debian): `pipx install apm-cli`.
+- Manual: download the platform archive from the GitHub releases page, extract, place the binary on `PATH`.
+
+Verify with `apm --version`.
+
+## Install or manage an agent runtime
+
+Default:
+
+```bash
+apm runtime setup copilot
+```
+
+Other targets: `apm runtime setup codex`, `apm runtime setup gemini`, `apm runtime setup llm`.
+
+- `apm runtime list` — show installed runtimes.
+- `apm runtime status` — show which runtime `apm run` will pick by default.
+- `apm runtime remove <name> -y` — uninstall without an interactive prompt.