vNext: Split the README into a docs library with user documentation

[RobHofmann]

What

The README had grown to 220 lines and mixed installation, configuration, protocol details and entity descriptions. It is now a short entry point: badges, a documentation block, a "why" section, a quick start with My Home Assistant buttons, the issue policy, help and support, contributing, a development note, license and credits.

The content moved to docs/, which now holds user documentation next to the developer documentation. docs/README.md is the index for both.

File	Covers
docs/installation.md	Requirements, HACS, manual install, Wi-Fi setup links, moving from 4.x
docs/configuration.md	Every flow step and option with its default, reconfigure, device removal, automatic IP updates, YAML rules and MAC keys
docs/connection-methods.md	Local, cloud and mixed setups, the config entries, VRF units
docs/entities.md	Climate, sensors, switches, selects and numbers, the mode each one needs, availability, state restore
docs/actions.md	get_prop_values, get_prop_values_all, the response shape, diagnostics download
docs/automation-examples.md	Seven automations and a script, with the real entity names and the current automation syntax
docs/encryption-key.md	When the key is not found by itself and how to get it
docs/troubleshooting.md	The time out policy, debug logging, repair issues, flow messages, common situations, how to report a bug

Issue policy

Added the "Issues" section from the master README about TimeOut and Cannot connect reports, with its link to issue 405. It is in the README and at the top of docs/troubleshooting.md.

Badges and CI

Release, license, Validate and Lint badges next to the HACS and Home Assistant badges. The workflow badges follow the default branch, so nothing needs to change when 5.0 lands on master.

The Lint badge needs a workflow, so .github/workflows/lint.yml is new. It runs ruff check and ruff format --check on Python 3.14 on every push and PR. Pylint and Mypy stay local, because they need the Home Assistant core checkout that only the devcontainer has. Ruff passes on the whole tree today. docs/development.md describes the job.

Corrections

The old text was checked against the code and against the dev instance. These were wrong and are now correct in the docs:

• The climate attribute is current_outside_temperature, not outside_temperature.
• Temperature Step is a device option, not an entity.
• The YAML default for features is every feature except humidity_control. manual-configuration.yaml said "all options"; fixed there too.
• Turbo is limited to Cool and Heat. Turbo and Quiet are both ignored while Power Save or Smart Heat is on.
• Entity IDs depend on the UI language of the Home Assistant instance, because they are built from the translated entity name. A Dutch instance gets switch.<device>_pieptoon for the beeper. The Smart Heat 8ºC switch becomes smart_heat_8oc.

Also

• The bug report template linked the debugging section of a fork's README. It now links docs/troubleshooting.md.
• AGENTS.md points agents to the user docs when a change touches something a user can see.
• Three em dashes in supported-devices.md replaced.
• The LLM line from the credits moved into the development note.

Checks

• Every relative link and anchor in the changed docs resolves.
• No em dashes in the changed files.
• Ruff check and format pass on the whole tree, so the new Lint job starts green.
• No code or behavior change, nothing to test on a device.

Found, not fixed

config_flow.py sets the error cannot_connect_mqtt, but en.json has no such key, so an MQTT failure in the flow shows the raw key. Worth a separate PR.