revert(popover): drop auto-anchor min-width default; keep content-driven sizing

Yesterday's checkpoint normalized popover min-width to the floating anchor
width across all components, then re-anchored pickers to their input
wrapper so the rule would line popover ≥ input. Tested at /uix/components/
date-picker the result was a popover stretched to 458 px (input width)
while the calendar inside is only ~268 px — leaving an empty band to the
right of every row.

After re-checking the industry research:
- Radix / shadcn / React Aria popovers default to INTRINSIC content width
  and expose `--*-trigger-width` as opt-in.
- Ark UI only auto-matches via `positioning.sameWidth` (opt-in).
- bits-ui Select is the only one that bakes width matching by default.

Conclusion: forcing min-width = anchor-width across all popovers is wrong;
each picker's content has its own intrinsic width that should drive the
popover. Reverting the normalization to the previous (Radix-style)
content-driven default. The Select + Combobox `matchAnchorWidth = true`
default is preserved (those are listbox-style popovers where the trigger
width is a sensible reference) and the sideOffset=6 normalization stays.

Files reverted:
- src/uix/eidos/components/popover/popover.css: removed
  `--_popover-min-width: var(--floating-anchor-width)` default.
- src/uix/eidos/components/date-picker/date-picker-content.svelte:
  restored `--_popover-content-min-width-override: max-content` default
  and dropped the `customAnchor={picker.inputRef.current}` wiring.
- src/uix/eidos/components/date-picker/date-picker.css: restored
  `min-inline-size: max-content` on the calendar/grid popover rules.
- src/uix/soma/components/date-picker/date-picker-provider.svelte.ts:
  removed `inputRef` + `setInputRef`.
- Removed src/uix/{soma,eidos}/components/date-picker/date-picker-input.svelte.
- src/uix/{soma,eidos}/components/date-picker/{exports,index}: revert
  `Input` to the DateField re-export.

Kept from yesterday:
- sideOffset = 6 default in popover-content + 5 pickers (genuine
  normalization, no width tension).
- Select/Combobox matchAnchorWidth = true (listbox convention).
- floating.svelte.ts `opts.style.current` bug fix (was preventing
  any consumer style from reaching the popover wrapper).
- Combobox single-mode auto-sync of inputValue to selected label.

Verified at /uix/components/date-picker: popover renders at 268 px
(calendar content width), aligned end of the 458 px input — matches the
Radix-style behaviour we now consider canonical.

svelte-check --threshold error → 0 errors / 0 warnings / 4584 files.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/uix/eidos/components/popover/popover.css

@@ -85,20 +85,12 @@
 		--_popover-content-max-height-override,
 		var(--floating-available-height, calc(100dvh - var(--space-4)))
 	);
-	/* Normalized floor — popover layer is NEVER narrower than the anchor
-	   (input / trigger / button it was launched from). Content that wants
-	   to grow beyond still can via `inline-size`. Consumers that should
-	   opt out (tooltip, dialog) override this to `auto`. */
-	--_popover-min-width: var(
-		--_popover-content-min-width-override,
-		var(--floating-anchor-width, auto)
-	);
 
 	display: grid;
 	box-sizing: border-box;
 	gap: var(--popover-gap);
 	inline-size: min(var(--_popover-width), var(--_popover-max-width), calc(100vw - var(--space-4)));
-	min-inline-size: var(--_popover-min-width);
+	min-inline-size: var(--_popover-content-min-width-override, auto);
 	max-inline-size: min(var(--_popover-max-width), calc(100vw - var(--space-4)));
 	block-size: var(--_popover-content-height-override, auto);
 	min-block-size: var(--_popover-content-min-height-override, auto);