feat: add achievements system, hint overlay, and progress page polish

Achievements system:
- Add src/lib/server/milestones.ts with full achievement definitions and
  calculation logic (16 achievements: streaks, book set completions,
  community milestones like Overachiever/Procrastinator/Outlier, and fun
  ones like Prodigal Son, Extra Credit, Is This A Joke To You?)
- Wire calculateMilestones() into the progress page server load
- Replace the old ad-hoc milestone cards with a proper achievements grid
  (3/4 col, uniform min-height cards, larger text)
- Change "With God, All Things Are Possible" from "every game solved in 1"
  to "solve in 1 guess for each of the 66 books at least once"

Game page hint overlay:
- After a correct testament/section/first-letter match, display a subtle
  text hint below the verse prompt (e.g. "It is in the Old Testament.")
- Hints fade in 2.8s after a guess (after the row flip animation)
- Hints are only shown to new players (fewer than 3 tracked wins) to
  avoid being patronising to experienced players

Progress page:
- Hide Skill Growth chart with {#if false && showChart} pending rework
- Fix book tier colour scheme: explored=blue, mastered=purple, perfect=emerald
  (was amber/emerald — now consistent across grid, legend, and stat cards)
- Simplify GuessesTable row colour: remove proximity gradient, use flat red
  for wrong guesses
- Add "Come back tomorrow!" encouragement text in CountdownTimer for new
  players (fewer than 3 wins)
- Fix GamePrompt text colour to always be gray-100

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

src/routes/+page.svelte

@@ -2,6 +2,7 @@
 	import type { PageProps } from "./$types";
 	import { browser } from "$app/environment";
 	import { enhance } from "$app/forms";
+	import { onMount } from "svelte";
 
 	import VerseDisplay from "$lib/components/VerseDisplay.svelte";
 	import SearchInput from "$lib/components/SearchInput.svelte";
@@ -13,7 +14,7 @@
 	import DevButtons from "$lib/components/DevButtons.svelte";
 	import AuthModal from "$lib/components/AuthModal.svelte";
 
-	import { evaluateGuess } from "$lib/utils/game";
+	import { evaluateGuess, getFirstLetter } from "$lib/utils/game";
 	import {
 		generateShareText,
 		shareResult,
@@ -75,6 +76,62 @@
 			!persistence.chapterGuessCompleted,
 	);
 
+	let knownTestament = $derived(
+		persistence.guesses.some((g) => g.testamentMatch)
+			? correctBook?.testament
+			: null,
+	);
+	let knownSection = $derived(
+		persistence.guesses.some((g) => g.sectionMatch)
+			? correctBook?.section
+			: null,
+	);
+	let knownFirstLetter = $derived(
+		persistence.guesses.some((g) => g.firstLetterMatch)
+			? getFirstLetter(correctBook?.name ?? "").toUpperCase()
+			: null,
+	);
+
+	let testamentVisible = $state(false);
+	let sectionVisible = $state(false);
+	let firstLetterVisible = $state(false);
+	let showHints = $state(false);
+
+	// On page load, show hints that are already known without animation
+	onMount(() => {
+		if (knownTestament) testamentVisible = true;
+		if (knownSection) sectionVisible = true;
+		if (knownFirstLetter) firstLetterVisible = true;
+
+		const winCount = Object.keys(localStorage).filter(
+			(k) => k.startsWith("bibdle-win-tracked-") && localStorage.getItem(k) === "true"
+		).length;
+		showHints = winCount < 3;
+	});
+
+	// Fade in newly revealed hints after the guess animation completes
+	$effect(() => {
+		if (!knownTestament || testamentVisible) return;
+		const id = setTimeout(() => {
+			testamentVisible = true;
+		}, 2800);
+		return () => clearTimeout(id);
+	});
+	$effect(() => {
+		if (!knownSection || sectionVisible) return;
+		const id = setTimeout(() => {
+			sectionVisible = true;
+		}, 2800);
+		return () => clearTimeout(id);
+	});
+	$effect(() => {
+		if (!knownFirstLetter || firstLetterVisible) return;
+		const id = setTimeout(() => {
+			firstLetterVisible = true;
+		}, 2800);
+		return () => clearTimeout(id);
+	});
+
 	async function submitGuess(bookId: string) {
 		if (persistence.guesses.some((g) => g.book.id === bookId)) return;
 
@@ -318,6 +375,42 @@
 				<div class="animate-fade-in-up animate-delay-400">
 					<GamePrompt guessCount={persistence.guesses.length} />
 
+					{#if showHints && (knownTestament || knownSection || knownFirstLetter)}
+						<div
+							class="text-xs uppercase tracking-widest font-bold text-center text-gray-500 dark:text-gray-400 flex flex-col gap-1 mb-4 -mt-2"
+						>
+							{#if knownTestament}
+								<p
+									style="transition: opacity 0.5s ease; opacity: {testamentVisible
+										? 1
+										: 0};"
+								>
+									It is in the {knownTestament === "old"
+										? "Old"
+										: "New"} Testament.
+								</p>
+							{/if}
+							{#if knownSection}
+								<p
+									style="transition: opacity 0.5s ease; opacity: {sectionVisible
+										? 1
+										: 0};"
+								>
+									It is in the {knownSection} section.
+								</p>
+							{/if}
+							{#if knownFirstLetter}
+								<p
+									style="transition: opacity 0.5s ease; opacity: {firstLetterVisible
+										? 1
+										: 0};"
+								>
+									The book's name starts with "{knownFirstLetter}".
+								</p>
+							{/if}
+						</div>
+					{/if}
+
 					<SearchInput
 						bind:searchQuery
 						{guessedIds}
@@ -356,7 +449,9 @@
 			</div>
 
 			{#if isWon}
-				<hr class="animate-fade-in-up animate-delay-800 border-gray-300 dark:border-gray-600" />
+				<hr
+					class="animate-fade-in-up animate-delay-800 border-gray-300 dark:border-gray-600"
+				/>
 				<div class="animate-fade-in-up animate-delay-800">
 					<a
 						href="https://discord.gg/yWQXbGK8SD"