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-releases/references/conventions.md

@@ -0,0 +1,44 @@
+---
+topic: conventions
+source_keys:
+  - context7-websites-gitea
+  - context7-gitea-tea-cli
+---
+
+# Release and tag conventions
+
+Practitioner conventions that inform *how* to use the mechanics in `call-signatures.md` — not
+additional tool schemas.
+
+## Release wraps a tag, not the reverse
+
+A release is a title, body (notes), and draft/prerelease flags layered on top of an existing or
+newly-created tag. The tag is the git-level object (a name pointing at a commit); the release is a
+Gitea-level metadata wrapper around it. This is why `delete_release` and `delete_tag` are separate
+calls with separate identifiers (numeric id vs. tag name) — removing the wrapper never implies
+removing the underlying pointer, and vice versa.
+
+## Semver tag naming
+
+Per the `tea` CLI (the reference Gitea client), tag names conventionally follow semver with a `v`
+prefix: `v1.2.0`, `v2.0.0-beta.1`. This is a convention observed by tooling and humans, not a
+Gitea-enforced constraint — the API accepts any string as `tag_name`. Don't validate or rewrite a
+caller-supplied tag name against semver; just pass it through.
+
+## Draft and prerelease are explicit flags
+
+`is_draft` and `is_pre_release` are booleans the caller sets directly on `create_release` — Gitea
+does not infer either from the tag name, even though the `-beta`/`-rc` suffix convention above is
+commonly used to signal a prerelease to humans. When a user asks to "cut a beta" or "publish a
+release candidate," set `is_pre_release: true` explicitly in the same call rather than relying on
+the tag string to carry that meaning.
+
+Note the input/output naming mismatch: the input param is `is_draft`, but the release object
+returned by the API uses `draft` (and `prerelease`) as the field names. `draft` is never a valid
+input key — passing `draft: true` to `create_release` is silently ignored rather than erroring.
+
+## Release notes sourcing
+
+Practitioner convention (per `tea`) is to source release notes (`body`) from a changelog file
+rather than typing them inline for each release — useful context when a caller asks to "generate"
+or "use the changelog for" release notes rather than write them from scratch.