docs: cover pre-2026.6 automation, helper, dashboard & scene gaps

[kingpanther13]

What does this PR do?

Fills coverage gaps in the home-assistant-best-practices skill that predate HA 2026.6 — native constructs that have existed for releases but the skill never documented. Closes #50, and folds in additional verified gaps found while auditing the referenced files.

references/automation-patterns.md

• Trigger Types: zone, template, calendar, webhook, homeassistant, conversation, tag, geo_location, persistent_notification triggers; a "fire an event" action note paired with the event trigger
• Native Conditions: condition: trigger; a condition: device caveat on the device trigger
• New sections: Parallel Actions (parallel: vs mode: parallel), Stopping a Sequence (stop:), Variables (variables: / trigger_variables:), Capturing Action Responses (response_variable); a delay: action entry; per-element enabled:

references/helper-selection.md

• trend, bayesian (new Probabilistic Inference section), and mold_indicator helpers (+ TOC and decision-matrix rows)
• "How Helpers Are Created": the storage-collection vs config-entry-flow distinction (framed in HA APIs, not tool names)

references/dashboard-guide.md

• Dashboard strategies + "Take control"; grid_options card sizing; heading card; markdown card; object/typed badge form; expanded visibility conditions (incl. screen); dropped the stale (2024+) heading qualifier

references/scenes.md (new)

• Scene config shape, scene.turn_on/create/apply/reload, and the snapshot-vs-script distinction; wired into SKILL.md and README.md

Every added snippet was verified against the current home-assistant.io docs and, where relevant, home-assistant/core source (multi-agent adversarial review). Tool-agnostic throughout — no MCP tool names — per CONTRIBUTING.

Checklist

• Tested with real scenarios (if changing skill content) — syntax verified against live HA 2026.6 docs + core source; not yet exercised on a live instance
• README.md Skill Contents table updated (if reference files were added or removed) — added references/scenes.md

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request introduces comprehensive updates to the Home Assistant best practices documentation, including a new reference guide for Scenes (scenes.md) and extensive additions to the automation patterns, dashboard guide, and helper selection references. The reviewer's feedback focuses on optimizing token-efficiency for LLMs by suggesting that bulleted lists in helper-selection.md, scenes.md, and dashboard-guide.md be converted into comma-separated paragraphs.

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[kingpanther13]

@sergeykad sorry I forgot to mark these as ready, both this one and #60 are ready for review.