Add write/edit schema-repair plugin and documentation

Keeps OpenCode's write and edit tools usable with OpenAI-compatible local
models, instead of disabling them as the issue thread suggests.

- tool.execute.before renames known alias keys in place before the schema
  decode, so a call using fileContent/path instead of content/filePath
  succeeds rather than failing validation and looping. Covers write, edit,
  bash, read, grep and glob, and never overwrites a key the model got right
- tool.definition re-emits the write schema with filePath before content, so a
  model that exhausts its output budget mid-content has already emitted the
  required path
- Logs to ~/.local/share/opencode/plugin-schema-fix.log so it is possible to
  confirm the plugin actually loaded and see what it repaired

README documents the two distinct causes behind the same SchemaError message,
since only one of them is a plugin problem: mis-keyed arguments, which this
fixes, and empty {} arguments, which come from context overflow when a custom
provider leaves limit.context at 0 and auto-compaction never fires. The latter
needs provider limits in the config, not a plugin.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NADzsbQyEBxJGgh4Ueatoa