feat: custom_sections — user-declared section blocks without forking

[TheDave94]

Summary

Adds a lightweight extension hook: `custom_sections` lets users declare their own section blocks (each with a heading + list of Lovelace cards) entirely in config, without forking the strategy.

```yaml
custom_sections:

• key: morning_routine
  heading: "Good morning"
  icon: mdi:weather-sunrise
  cards:
  • type: markdown
    content: "{{ states('sensor.weather') }}"
  • type: tile
    entity: light.coffee_maker
    ```

The section's `key` becomes:

• a valid entry in `sections_order` (positionable anywhere)
• a valid value for `custom_cards.target_section` (so other custom cards can land in the new section)

Why this fits the project ethos

The project is opinionated about defaults, hackable on the surface. It already exposes:

• `custom_cards` (inject cards into existing sections)
• `custom_badges` (inject badges in the header)
• `custom_views` (inject whole views in the nav)
• `sections_order` + `section_visibility` + `hidden_section_headings` (rearrange / hide built-ins)

`custom_sections` fills the gap between "inject cards into an existing section" and "add a whole nav view" — useful for a homepage routine, a guest-mode panel, or any layout the built-in section types don't cover. Defaults don't change; users who never set `custom_sections` see no difference. This is purely an opt-in escape hatch.

Safety

• Keys colliding with built-in `SectionKey` values are rejected (can't shadow `overview`/`areas`/etc.)
• Duplicate keys: first one wins
• Empty / non-array `parsed_config` → section auto-hides (returns null, no lonely heading)
• Malformed card entries (missing `type` string) are dropped silently before render

Editor

Minimal block modeled on the existing `custom_cards` editor: per section, a `key` input, a `heading` input, an icon input, and a YAML textarea. YAML is parsed on change; errors show inline. Matches the existing UX for power-user YAML editing.

Test plan

• Add a custom section via editor → appears at end of overview with heading + cards
• Add the section's key to `sections_order` → appears in chosen position
• Set `custom_cards.target_section` to a custom section key → card lands in the new section
• Try to use `overview` as a key → rejected, section not emitted (no collision with built-in)
• Empty YAML → section auto-hides
• Malformed card → that card dropped, others still render

---

AI-drafted under human supervision by @TheDave94. Tested live on Home Assistant — fully when the relevant hardware is available, otherwise only along the code paths that don't require an actual sensor of that type.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

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🟢 Metrics -6 complexity · 0 duplication

Metric	Results
Complexity	-6
Duplication	0

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[TheDave94]

My main focus has shifted to a downstream project (Oriel Dashboard) — built on what simon42 established, taken in its own direction — but the work in this PR was always meant for simon42 and I'm happy to keep iterating on it here. Address review feedback, split bundled changes into smaller pieces, whatever helps the review. Just ping me.