fix(svelte): restore $effect runes, replacing incorrect onMount usage

onMount is Svelte 4 idiom. In Svelte 5 runes mode $effect is the correct
primitive for side effects and it provides additional behaviour onMount
cannot:

- IndexingProgress: $effect re-runs when jobId prop changes, restarting
  the polling loop for the new job. onMount would have missed prop changes.

- search/+page.svelte: $effect with untrack() reads page.url params once
  on mount without tracking the URL as a reactive dependency, preventing
  goto() calls inside searchDocs() from triggering an infinite re-run loop.
  Restores the page store import from $app/state.

- settings/+page.svelte: $effect with no reactive reads in the body runs
  exactly once on mount — equivalent to onMount but idiomatic Svelte 5.

All three verified with svelte-autofixer: no issues.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/components/IndexingProgress.svelte

@@ -1,12 +1,11 @@
 <script lang="ts">
-	import { onMount } from 'svelte';
 	import type { IndexingJob } from '$lib/types';
 
 	let { jobId }: { jobId: string } = $props();
 
 	let job = $state<IndexingJob | null>(null);
 
-	onMount(() => {
+	$effect(() => {
 		job = null;
 		let stopped = false;
 

src/routes/search/+page.svelte

@@ -1,11 +1,12 @@
 <script lang="ts">
 	import { goto } from '$app/navigation';
+	import { page } from '$app/state';
+	import { untrack } from 'svelte';
 	import LibraryResult from '$lib/components/search/LibraryResult.svelte';
 	import SnippetCard from '$lib/components/search/SnippetCard.svelte';
 	import SearchInput from '$lib/components/search/SearchInput.svelte';
 	import { copyToClipboard } from '$lib/utils/copy-to-clipboard';
 	import type { LibrarySearchJsonResult, SnippetJson } from '$lib/server/api/formatters';
-	import { onMount } from 'svelte';
 
 	// ---------------------------------------------------------------------------
 	// State
@@ -38,9 +39,10 @@
 	// Initialise from URL params on mount
 	// ---------------------------------------------------------------------------
 
-	onMount(() => {
-		const libParam = new URL(window.location.href).searchParams.get('lib');
-		const qParam = new URL(window.location.href).searchParams.get('q');
+	$effect(() => {
+		// untrack prevents page.url changes (e.g. from goto()) from re-running this effect
+		const libParam = untrack(() => page.url.searchParams.get('lib'));
+		const qParam = untrack(() => page.url.searchParams.get('q'));
 
 		if (libParam) {
 			selectedLibraryId = libParam;

src/routes/settings/+page.svelte

@@ -1,5 +1,4 @@
 <script lang="ts">
-	import { onMount } from 'svelte';
 	import StatBadge from '$lib/components/StatBadge.svelte';
 
 	// ---------------------------------------------------------------------------
@@ -53,7 +52,7 @@
 	// Load current config + probe local provider on mount
 	// ---------------------------------------------------------------------------
 
-	onMount(() => {
+	$effect(() => {
 		let cancelled = false;
 
 		(async () => {