Unify contribution guidance

Consolidate human and coding-agent instructions in CONTRIBUTING.md, with
AGENTS.md and CLAUDE.md linking to the shared guide.

Remove volatile package inventories, align the Markdown and issue-writing
rules, and document multi-runtime vocabulary snapshot updates in the guide,
the vocab-tools README, and the add-vocab skill.

Assisted-by: Codex:gpt-5.6-sol

Author: dahlia

.agents/skills/add-vocab/SKILL.md

@@ -7,7 +7,6 @@ description: >-
   implementing FEPs, extending ActivityStreams vocabulary, or adding third-party
   vocab types such as Mastodon extensions, Litepub types, or other fediverse
   vocabularies.
-version: 1.0.0
 ---
 
 Adding vocabulary to @fedify/vocab
@@ -52,12 +51,17 @@ Workflow
 5.  If a new context URL is needed, add it to
     `packages/vocab-runtime/src/contexts.ts`
 6.  Run `mise run codegen` to generate TypeScript classes
-7.  Run `mise run check` to verify everything compiles
-8.  Ask the user to review the YAML definition and generated code carefully
+7.  Run `mise run test:update_snapshots` to update the Deno, Node.js, and Bun
+    snapshots
+8.  Run `mise run check` to verify everything compiles
+9.  Ask the user to review the YAML definition and generated code carefully
     before committing
 
 The generated TypeScript class is automatically exported from `@fedify/vocab`
 via `packages/vocab/src/vocab.ts` (generated) and `packages/vocab/src/mod.ts`.
+The `@fedify/vocab-tools` snapshots are stored separately for Deno, Node.js,
+and Bun.  Always update all three with the aggregate task when generated output
+changes; do not update only one runtime's snapshot.
 
 
 YAML file format

.hongdown.toml

@@ -1,12 +1,13 @@
 no_inherit = true
 include = ["*.md", "**/*.md"]
 exclude = [
+  ".git/**",
   "**/node_modules/**",
   "**/dist/**",
   ".agents/skills/**",
   ".claude/skills/**",
   ".github/copilot-instructions.md",
-  "AGENT.md",
+  "AGENTS.md",
   "CLAUDE.md",
   "GEMINI.md",
   "WARP.md",