docs: prepare v0.4.0 release

Rewrite the README around the supported public API, add a public API
stability policy, document the deprecation timeline, and refresh the
CHANGELOG with the full 0.4.0 scope. Add a short CONTRIBUTING guide.
Apply minor pending fixes to LICENSE and .env.example. Fix a couple of
verify=False antipatterns in the docs/ pages.

README:
- Badges (PyPI version, Python versions, license, CI).
- Quick start that actually runs (no missing import, no global
  disable_warnings, correct VYDEVICE_VERIFY_SSL parse).
- Environment variable table with defaults.
- ApiResponse contract documented as a dataclass.
- Compact API overview (configure / retrieve / show / generate / reset /
  config-file / system / image).
- Public API stability section with the 0.4 -> 0.5 -> 0.6 -> 1.0
  deprecation timeline.
- Logging section: NullHandler default, pyvyos logger, redacted key.
- VyOS compatibility note (1.4 LTS, 1.5 rolling).
- Development with uv; optional pre-commit.

CHANGELOG:
- Consolidated 0.4.0 entry covering both the architecture refactor and
  this cleanup, since 0.4.0 was tagged in git but never published.
- Explicit Added / Changed / Removed / Fixed / Compatibility / Notes
  sections.
- 0.3.0 entry annotated as 'tagged but never released to PyPI'.

CONTRIBUTING.md:
- Scope statement (thin HTTPS API wrapper).
- Pull request rules; explicit 'do not change HTTP payload in passing'.
- Development setup with uv.
- Public API stability summary.

Fixes from the previous review-fixes branch:
- LICENSE copyright now reads 'GravScale, Roberto Berto'.
- .env.example default flipped to VYDEVICE_VERIFY_SSL=true with
  field descriptions.
- docs/getting-started.md: VERIFY_SSL default to true; urllib3
  disable_warnings now passes the specific InsecureRequestWarning.
- docs/index.md: quick example uses verify=True; removed RTD link
  (RTD config was removed in this release because the build never
  worked).

1 files changed, 71 insertions, 0 deletions

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+# Contributing to pyvyos
+
+Thanks for considering a contribution. `pyvyos` is a small library with a
+narrow scope, which makes review and maintenance easier when contributions
+follow a few simple rules.
+
+## Scope
+
+`pyvyos` is a thin Python wrapper around the VyOS HTTPS API. Changes that
+fit naturally into this scope are welcome. Anything that adds a new
+dependency, introduces a parallel client (SSH, NETCONF, …), or expands
+beyond the HTTPS API surface is best discussed in an issue first.
+
+## Before opening a pull request
+
+1. **Open an issue first** for anything beyond a small fix or a typo. It
+   saves everyone time if the direction is agreed before the patch lands.
+2. **Keep the diff focused.** One topic per pull request. Refactors and
+   bug fixes are easier to review separately.
+3. **Do not change HTTP payload generation in passing.** Payload changes
+   require a deliberate review pass; they should be their own pull
+   request and include tests.
+4. **Run the test suite locally:** `uv run pytest`.
+5. **Match the existing style.** No formatter is enforced yet; just keep
+   diffs minimal and readable.
+
+## Development setup
+
+```bash
+git clone https://github.com/vyos-contrib/pyvyos.git
+cd pyvyos
+uv sync --extra dev
+uv run pytest
+```
+
+Optional pre-commit hooks (whitespace, EOF, YAML/TOML syntax):
+
+```bash
+pip install pre-commit
+pre-commit install
+```
+
+## Public API stability
+
+The supported public API is:
+
+```python
+from pyvyos import VyDevice, ApiResponse
+```
+
+Compatibility shims at `pyvyos.device` and `pyvyos.rest` are kept while
+the cost is trivial. Anything under `pyvyos.core.*` is internal and may
+change between minor releases.
+
+If your change touches the public API surface, please flag it explicitly
+in the pull request description.
+
+## Reporting bugs
+
+When reporting a bug, please include:
+
+- The `pyvyos` version (`pip show pyvyos`).
+- The Python version.
+- The VyOS version of the device.
+- A minimal reproducer and the resulting error (or, for behaviour bugs,
+  the observed vs expected behaviour).
+
+## License
+
+By contributing you agree that your contribution will be licensed under
+the [MIT License](LICENSE).