feat(pipe-coupling): rewrite as RNT Smart Clamp from Rano Tech

Replaced SMC content with RNT Smart Clamp (Rano Tech) per
supplier data from https://www.ranotech.com/rnt-smart-clamp/

Changes:
1 Content rewrite — pipe-coupling.astro now shows:
   - Hero: RNT Smart Clamp (แคลมป์รัดท่อ Rano Tech)
   - 5 product models with descriptions:
     * MJG — same-size coupling (ต่อท่อขนาดเท่ากัน)
     * MJH — repair clamp with hinge (ซ่อมรั่วแบบบานพับ)
     * MJD — hybrid repair/coupling (ไฮบริด)
     * MJER — elbow repair (ซ่อมส่วนโค้ง)
     * MJCX — custom series
   - FAQ section (4 questions)
   - Installation details

2) Images — Downloaded 12 real RNT product photos from
   ranotech.com/wp-content/uploads/ to
   public/images/pipe-coupling/. Old SMC images removed.

3) all-products.astro — Pipe Coupling card now uses smc-02.jpg
   (new RNT main image) instead of old BG-SMC02.png

4) Sitemap — pipe-coupling URL unchanged (no change needed)
EOF
)

public/images/pipe-coupling/SMC-Page-05.svg

@@ -1 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" width="400" height="300" viewBox="0 0 400 300"><rect width="400" height="300" fill="#65a30d"/><text x="200" y="150" text-anchor="middle" fill="white" font-family="sans-serif" font-size="18">Coupling 05</text></svg>

public/images/pipe-coupling/SMC-Page-07.svg

@@ -1 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" width="400" height="300" viewBox="0 0 400 300"><rect width="400" height="300" fill="#65a30d"/><text x="200" y="150" text-anchor="middle" fill="white" font-family="sans-serif" font-size="18">Coupling 07</text></svg>

public/images/pipe-coupling/coupling.svg

@@ -1,6 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" width="400" height="400" viewBox="0 0 400 400">
-  <rect width="400" height="400" fill="#65a30d"/>
-  <text x="200" y="100" text-anchor="middle" fill="white" font-family="sans-serif" font-size="24" font-weight="600">Pipe Coupling</text>
-  <ellipse cx="200" cy="250" rx="90" ry="30" fill="none" stroke="white" stroke-width="8"/>
-  <ellipse cx="200" cy="250" rx="60" ry="18" fill="none" stroke="white" stroke-width="4"/>
-</svg>