feat: configurable main icon→name gap via name_gap

[BlackZork]

Disclaimer

Changes in this PR and description below were entirely generated by Claude Code with my supervision only. Please verify. I needed to shorten the hard-coded 16px gap between main icon and main label. 16px is way to big for RPI 800x480 display.

Summary

Adds a card-level name_gap option (and a matching --multiple-entity-row-name-gap
CSS variable) that controls the horizontal spacing between the main entity's icon and the
row name.

type: custom:multiple-entity-row
entity: light.living_room
name_gap: 8px      # or a number (treated as px), or any CSS length / var(--x)

Default rendering is completely unchanged — the option is opt-in and a no-op when unset.

Motivation

That gap is HA core hui-generic-entity-row's .info padding-inline-start, hardcoded at
16px inside that element's own shadow DOM. It is not exposed as a CSS variable, padding
is not an inherited property, and styles from outside a shadow tree can't cross the boundary
(a theme or card-mod can't reach it). So today the icon→name spacing on a multiple-entity-row
simply can't be adjusted. On dense/compact dashboards (e.g. a wall-panel layout) 16px is often
too wide.

Because this card creates the hui-generic-entity-row it wraps, it can legitimately reach into
that child to expose the setting.

How it works

When (and only when) name_gap is set:

1. render() sets --multiple-entity-row-name-gap: <value> on the hui-generic-entity-row
   host (same mechanism as the existing icon_color → iconColorCss inline var).
2. updated() injects a one-time <style> into that child's shadowRoot:

   :host .info {
     padding-inline-start: var(--multiple-entity-row-name-gap, 16px);
     padding-left:         var(--multiple-entity-row-name-gap, 16px);
   }

Design points:

• :host .info (specificity 0,2,0), not !important. Core's static styles are applied via
  adoptedStyleSheets, which the cascade orders after a <style> appended to the shadow root —
  so an equal-specificity rule would lose. Higher specificity wins regardless of order, and leaving
  !important off means a user's own override still wins.
• Both logical + physical padding are set, so it also applies under RTL.
• 16px fallback in the var() keeps the default byte-for-byte identical.
• Gated on name_gap — rows that don't use it get zero shadow modification and no injected
  style at all.
• The injected rule is static (reads the variable), so changing name_gap later only updates the
  host variable via re-render; no re-injection. Injection is idempotent (guarded by a marker attr).
• A number is treated as px; a string passes through (8px, 0.5em, var(--x)); 0 is honored.

Changes

• src/types.ts — name_gap?: string | number on MultipleEntityRowConfig.
• src/entity.js — nameGapCss() helper (alongside iconColorCss).
• src/index.js — host variable in render(); updated() shadow injection.
• src/editor_schemas.ts — name_gap field + label in the visual editor (Main tab).
• README.md — options table row + a Theming section entry documenting the variable.
• src/index.test.js — unit tests for the host-variable half (see note below).

Testing

• yarn lint clean, full vitest suite passes (161 tests, incl. 4 new name_gap cases).
• The unit tests cover the host-variable side (number→px, string passthrough, 0 honored, omitted
  when unset). The deep shadow injection can only be exercised against a real core
  hui-generic-entity-row (the jsdom stub has no shadow), so it's verified at runtime rather than
  in the suite.
• Verified live on Home Assistant 2025.10.3: with name_gap: 5px/8px the row's core .info
padding-inline-start computes to the configured value across multiple rows; unset rows stay at
  16px; toggling the value updates it without re-injection; default rows are untouched.

Notes

• Fully backward compatible; no change for existing configs.
• Min HA unchanged (works on current stable; uses only hui-generic-entity-row internals already
  relied upon for the main row).

[jpettitt]

Thanks — this is a well-put-together PR, and the shadow-injection analysis is correct (verified against the current frontend bundle: .info{padding-left:16px;padding-right:8px;flex:30%;padding-inline:16px 8px}, no variable exposed).

One fix needed: the injected padding-left line breaks RTL rather than supporting it. Core's end-padding is 8px (padding-inline: 16px 8px); in RTL, padding-left is the inline-end side, so your rule overrides that 8px with the gap value. padding-inline-start alone is correct in both directions (universally supported on any browser running HA 2024.4+, this card's minimum) — please drop the physical property and the RTL sentence from the comment.

Happy to merge with that change.