feat(opencode): add language-specific coding skills

- add conventions for Bash, C#, Go, Python, and TypeScript
- add frontend guidance for HTMX, PrimeVue, and Vue
- document formatting, typing, testing, async, and framework-specific practices
- reference official documentation for framework API details

.config/opencode/skills/python/SKILL.md

@@ -0,0 +1,23 @@
+---
+name: python
+description: Python conventions (PEP 8, ruff, type hints). Use when editing .py files.
+---
+
+# Python Conventions
+
+## Style
+- Follow PEP 8; run `ruff check` and `ruff format` for linting and formatting.
+- Let ruff manage line length and import ordering; do not hand-format against it.
+
+## Typing
+- Add type hints on all function signatures; prefer modern syntax (`list[int]`, `X | None`) on supported Python versions.
+- Use `dataclasses` (or Pydantic where validation is required) for structured data.
+- Prefer an explicit exception hierarchy over bare `except:`.
+
+## Idioms
+- Prefer `pathlib.Path` over `os.path`.
+- Use f-strings for interpolation; use the `logging` module with structured handlers instead of `print` in libraries.
+- Prefer comprehensions and generator expressions over manual loops where readability is preserved.
+
+## Testing
+- Use `unittest` (or `pytest` if the project adopts it); mirror the source layout under a `tests/` directory.