fix(x-select): make .value reflect the current selection

[avanelsas]

Problem

x-select.value returned the value attribute, which a user selection never updates (only the inner <select> + the dispatched select-change event change). So any consumer reading el.value saw a stale value:

• The demo's status filter reads (.-value sel) → never sees the selection → looks dead.
• x-form's collect-values reads (.-value field) at submit and doesn't listen for select-change → forms silently submit the pre-selection value for x-select fields (latent; no e2e selected an option before submitting).

x-select was the only form control like this — x-form-field, x-checkbox, x-date-picker, etc. all make .value/.checked reflect the current value, which is the contract x-form relies on (and native <select>.value behaviour).

Fix

Override x-select's value getter to read the live inner <select>, with one disambiguation: a non-empty value set before its <option> exists (async-loaded options) is surfaced as pending via the attribute until the option arrives and apply-model! selects it.

This preserves both existing tests unmodified:

• value-attr-not-auto-set-on-change-test — a user change still updates only the inner <select>, never the attribute.
• string-property-value-test — el.value set before options reads back from the attribute.

And adds two regression tests: selection reflection, and set-before-options pending→resolves.

Verification

• clj-kondo clean
• full karma 5190 (the two new tests; no x-form/x-select regressions)

Stable-component fix → targets main. (Already cherry-picked onto the alpha branch so the demo's filter works there too.)

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