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/agent-author/assets/templates/apm-agent.md

@@ -0,0 +1,54 @@
+---
+<!-- Vendor-neutral APM agent definition (plugin/APM scope).
+     Path: <package-root>/.apm/agents/<name>.agent.md — one file, no counterpart.
+     `apm compile` copies this frontmatter verbatim to BOTH the Claude Code and
+     Copilot CLI targets — there is no per-target field integrator. Claude's
+     `tools:` (space-separated string) and Copilot's `tools:` (alias list) are
+     incompatible vocabularies, and Claude-only fields (isolation, maxTurns,
+     effort, memory, permissionMode) have no Copilot equivalent. A value correct
+     for one harness is guaranteed wrong on the other, so this scope carries
+     ONLY the fields below — full stop (see ADR-0016). `source_keys` is
+     provenance metadata, not a runtime field, and is exempt from that rule.
+
+     Do NOT add: tools, isolation, maxTurns, effort, memory, permissionMode,
+     disallowedTools, skills, color, initialPrompt, background, hooks, or
+     mcpServers. Omitting `tools` means inherit-all-tools on both harnesses,
+     which is never wrong.
+
+     Fill in all FILL IN: placeholders. Delete template comments before shipping. -->
+
+name: AGENT_NAME
+<!-- Required. Lowercase letters and hyphens only. Must be unique within the scope. -->
+
+description: FILL IN: Action-first description of what this agent does and when to invoke it.
+<!-- Required. The primary signal for autonomous delegation.
+     Start with a verb: "Reviews...", "Analyzes...", "Generates..."
+     Be specific about the triggering condition and expertise domain.
+     Example: "Reviews pull request diffs for security issues. Use proactively after code changes." -->
+
+<!-- model: sonnet
+     Optional. Aliases: sonnet, opus, haiku, fable. Or full model ID.
+     Omit to inherit the runtime default on whichever harness compiles this file. -->
+
+<!-- source_keys:
+       - slug-name
+     Development-only. Add when research sources informed this agent (slugs must match
+     sources.md at the package root — same directory as apm.yml).
+     Omit when no research was used. Not a runtime field — silently ignored by both harnesses. -->
+---
+
+FILL IN: System prompt body. Write as a direct role instruction.
+
+You are a FILL IN: role description. When invoked, FILL IN: primary action.
+
+## Inputs
+
+FILL IN: What inputs does this agent expect? (files, context, parameters)
+
+## Process
+
+FILL IN: Steps the agent takes. Be specific about ordering if it matters.
+
+## Output
+
+FILL IN: What does the agent produce? Format, location, structure.