feat(gitea): add gitea-files skill

Covers get_file_contents, get_dir_contents, get_repository_tree,
create_or_update_file, delete_file — all verified working with the
current write:issue/write:repository token scope.

plugins/gitea/skills/gitea-files/README.md

@@ -0,0 +1,23 @@
+# gitea-files
+
+Read and write individual files and directory/repository trees in a Gitea repository via the Gitea MCP server.
+
+## What it does
+
+This skill handles file-domain operations within the Gitea integration suite: reading a single file's contents, listing one directory level, walking a full repository tree (optionally recursive), creating or updating a file, and deleting a file. It owns the SHA-based optimistic-concurrency pattern that Gitea requires for file writes — the domain's sharpest gotcha — and defers branch creation, commit history, and pull request mechanics to `gitea-branches` and `gitea-prs`.
+
+## Usage
+
+```
+/gitea-files
+```
+
+Describe the file task: read a file or directory, walk a tree, create/update a file, or delete a file. Provide `owner`/`repo`/branch (or ask the user if not given) — this skill does not resolve them from a git remote itself.
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `SKILL.md` | Skill instructions for agents |
+| `references/examples.md` | Canonical call sequences: branch + file + PR, recovering a missing SHA before an update, deleting a file |
+| `references/sources.md` | Research sources backing the SHA/concurrency and direct-commit-vs-PR guidance |