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/gitea/skills/gitea-files/references/sources.md

@@ -0,0 +1,46 @@
+# Sources
+
+## gitea-mcp-repo
+
+**Description:** Official gitea-mcp repository (v1.3.0); operation/*.go source files documenting all 55 MCP tools, their parameters, and CLI flags.
+
+**Source:** https://gitea.com/gitea/gitea-mcp
+
+- **Research doc:** plugins/gitea/docs/research/docs/gitea/sources.md
+
+**Contributing files:**
+- SKILL.md (Gotchas, Reading, Writing — tool parameters and SHA/concurrency behavior, cross-checked live against the deployed MCP tool schemas via ToolSearch)
+- references/examples.md (canonical call sequences)
+
+## gitea-mcp-slim-go
+
+**Description:** Slim response shape structs from gitea-mcp source; defines exactly which fields the MCP server returns for files (top-level `sha`, no nested `content.sha`) and directory/tree entries.
+
+**Source:** https://gitea.com/gitea/gitea-mcp/raw/branch/main/operation/repo/slim.go
+
+- **Research doc:** plugins/gitea/docs/research/docs/gitea/sources.md
+
+**Contributing files:**
+- SKILL.md (Gotchas — top-level `sha` field location, `get_dir_contents`/`get_repository_tree` not being usable SHA sources for a file write)
+- references/examples.md (SHA-first update/delete sequences)
+
+## context7-websites-gitea
+
+**Description:** Official Gitea docs mirror on Context7 (docs.gitea.com content) — confirms direct-commit file editing through the web UI is a first-class, expected workflow rather than an API-only escape hatch.
+
+**Source:** context7:/websites/gitea
+
+- **Research doc:** plugins/gitea/docs/research/docs/gitea/sources.md
+
+**Contributing files:**
+- SKILL.md (Gotchas — "Direct commits to a branch are a first-class action, not a workaround")
+
+## context7-gitea-tea-cli
+
+**Description:** Official `tea` CLI (reference Gitea client) docs on Context7 — practitioner command patterns for issues, PRs, and releases, including semver tag/release conventions, draft/prerelease flags, and release-notes-from-file conventions. Consulted alongside `context7-websites-gitea` while researching `workflow-conventions.md` (both sources contribute to that research doc, backing `gitea-workflow`); its file-command patterns did not end up informing any gitea-files content.
+
+**Source:** context7:/git_gitea_com/gitea_tea
+
+- **Research doc:** plugins/gitea/docs/research/docs/gitea/sources.md
+
+**Contributing files:** (none)