feat(articles): visual upgrades — timeline, callouts, cards, severity pills

Add 4 reusable CSS article components and apply them across 6 cornerstone articles:

CSS (input.css):
- article-timeline: horizontal phase diagram with numbered cards, collapses to vertical on mobile
- article-callout (warning/tip/info): left-bordered callout boxes with icon and title
- article-cards: 2-col grid of accent-topped cards (success/failure/neutral/established/growth/emerging)
- severity: inline pill badges (high/medium-high/medium/low-medium/low) for risk tables

Articles updated:
- padel-hall-build-guide-en + padel-halle-bauen-de: ASCII code block → timeline HTML; 3 bold/blockquote warnings → callout boxes; success/failure patterns → 4 cards
- padel-hall-investment-risks-en + padel-halle-risiken-de: risk overview table severity → pills; personal guarantee section → callout; risk management section → 4 cards
- padel-hall-location-guide-en + padel-standort-analyse-de: market maturity paragraphs → 3 stage cards

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

data/content/articles/padel-hall-location-guide-en.md

@@ -148,11 +148,29 @@ The matrix also reveals where trade-offs are being made explicitly, which makes
 
 The 8 criteria above evaluate specific sites. But before shortlisting sites, it is worth stepping back to read the stage of the overall market — because the right operational strategy differs fundamentally depending on where a city sits in its padel development cycle.
 
-**Established markets**: Booking platforms show consistent peak-hour sell-out across most venues. Waiting lists are common. Demand is validated beyond doubt. The challenge here is elevated rent, elevated build costs, and entrenched operators who have already captured community loyalty. New entrants need a genuine differentiation angle — a superior facility specification, a better location within the city, or an F&B and coaching product that existing venues don't offer. Entry costs are high; returns, if execution is strong, are also high. Munich is the canonical German example.
-
-**Growth markets**: Demand is clearly building — booking availability tightens at weekends, new facilities are announced regularly, and the sport is gaining local media visibility. Supply hasn't caught up, so identifiable gaps still exist in specific districts or the surrounding hinterland. The risk profile is lower than in emerging markets, but the window for securing good real estate at reasonable rent is narrowing. The premium for moving decisively goes to those who arrive before the obvious sites are taken.
-
-**Emerging markets**: Limited current supply, a small but growing player base, and padel not yet mainstream enough to generate organic walk-in demand. Entry costs — rent especially — are lower. The constraint is that demand must be actively created rather than captured. Operators who succeed here invest in community: beginner programmes, local leagues, school partnerships, conversions from tennis clubs. The time to first profitability is longer, but the competitive position built in the first two years is often decisive for the long term.
+<div class="article-cards">
+  <div class="article-card article-card--established">
+    <div class="article-card__accent"></div>
+    <div class="article-card__inner">
+      <span class="article-card__title">Established markets</span>
+      <p class="article-card__body">Booking platforms show consistent peak-hour sell-out. Demand is validated. The challenge: elevated rent, high build costs, entrenched operators. New entrants need a genuine differentiation angle — superior spec, better location, or F&B and coaching that existing venues don't offer. Entry costs are high; returns, if execution is strong, are also high. Munich is the canonical German example.</p>
+    </div>
+  </div>
+  <div class="article-card article-card--growth">
+    <div class="article-card__accent"></div>
+    <div class="article-card__inner">
+      <span class="article-card__title">Growth markets</span>
+      <p class="article-card__body">Demand is clearly building — booking availability tightens at weekends, new facilities are announced regularly. Supply hasn't caught up; identifiable gaps still exist. The risk profile is lower, but the window for securing good real estate at reasonable rent is narrowing. The premium goes to those who arrive before the obvious sites are taken.</p>
+    </div>
+  </div>
+  <div class="article-card article-card--emerging">
+    <div class="article-card__accent"></div>
+    <div class="article-card__inner">
+      <span class="article-card__title">Emerging markets</span>
+      <p class="article-card__body">Limited supply, a small but growing player base, padel not yet mainstream. Entry costs — rent especially — are lower. The constraint: demand must be actively created rather than captured. Operators who succeed invest in community: beginner programmes, local leagues, school partnerships. Time to profitability is longer, but the competitive position built in the first two years is often decisive.</p>
+    </div>
+  </div>
+</div>
 
 Before committing to a site search in any city, calibrate where it sits on this spectrum. The 8-criteria framework then tells you whether a specific site works; market maturity tells you what kind of operator and strategy is required to make it work at all.