Projektin ZIP-lataus projektikorttiin

Lataa .zip -nappi renderöidään projektikortin headeriin.
ZIP rakennetaan selaimessa ilman ulkoisia kirjastoja (CRC-32 + ZIP-rakenne inline).
Kansiorakenne säilyy: prompts/*.md -tiedostot menevät alihakemistoon.

network-poc/frontend/src/pages/index.astro

@@ -1341,6 +1341,7 @@ OUTPUT FORMAT:
             `<span style="color:var(--purple);font-weight:600">${esc(name||'Projekti')} <span style="color:#8b949e;font-weight:normal">(${entries.length})</span></span>` +
             `<span style="display:flex;gap:6px">` +
             `<button class="btn btn-muted" onclick="copyAllProjectFiles('${id}')">Kopioi kaikki</button>` +
+            `<button class="btn btn-muted" onclick="downloadProjectZip('${id}','${esc(name||'projekti')}')">Lataa .zip</button>` +
             `<button class="btn btn-green" onclick="openInEditor(window._projectFiles['${id}'])">Avaa editorissa</button>` +
             `</span></div>` +
             `<div class="project-tabs">${tabs}</div>${panels}</div>`;
@@ -1360,6 +1361,84 @@ OUTPUT FORMAT:
         const text = Object.entries(files).map(([n,c]) => '# --- ' + n + ' ---\n' + c).join('\n\n');
         navigator.clipboard.writeText(text);
     };
+    window.downloadProjectZip = function(id, name) {
+        const files = window._projectFiles[id];
+        if (!files) return;
+        const enc = new TextEncoder();
+        const entries = Object.entries(files);
+        const localParts = [];
+        const centralParts = [];
+        let offset = 0;
+
+        for (const [fname, content] of entries) {
+            const nameBytes = enc.encode(fname);
+            const dataBytes = enc.encode(content);
+            const crc = crc32(dataBytes);
+
+            // Local file header
+            const local = new Uint8Array(30 + nameBytes.length + dataBytes.length);
+            const lv = new DataView(local.buffer);
+            lv.setUint32(0, 0x04034b50, true);  // signature
+            lv.setUint16(4, 20, true);           // version needed
+            lv.setUint16(8, 8, true);            // UTF-8 flag
+            lv.setUint32(14, crc, true);         // CRC-32
+            lv.setUint32(18, dataBytes.length, true); // compressed size
+            lv.setUint32(22, dataBytes.length, true); // uncompressed size
+            lv.setUint16(26, nameBytes.length, true); // filename length
+            local.set(nameBytes, 30);
+            local.set(dataBytes, 30 + nameBytes.length);
+            localParts.push(local);
+
+            // Central directory entry
+            const central = new Uint8Array(46 + nameBytes.length);
+            const cv = new DataView(central.buffer);
+            cv.setUint32(0, 0x02014b50, true);  // signature
+            cv.setUint16(4, 20, true);           // version made by
+            cv.setUint16(6, 20, true);           // version needed
+            cv.setUint16(8, 8, true);            // UTF-8 flag
+            cv.setUint32(16, crc, true);
+            cv.setUint32(20, dataBytes.length, true);
+            cv.setUint32(24, dataBytes.length, true);
+            cv.setUint16(28, nameBytes.length, true);
+            cv.setUint32(42, offset, true);      // local header offset
+            central.set(nameBytes, 46);
+            centralParts.push(central);
+
+            offset += local.length;
+        }
+
+        const centralSize = centralParts.reduce((s, c) => s + c.length, 0);
+        // End of central directory
+        const eocd = new Uint8Array(22);
+        const ev = new DataView(eocd.buffer);
+        ev.setUint32(0, 0x06054b50, true);
+        ev.setUint16(8, entries.length, true);
+        ev.setUint16(10, entries.length, true);
+        ev.setUint32(12, centralSize, true);
+        ev.setUint32(16, offset, true);
+
+        const blob = new Blob([...localParts, ...centralParts, eocd], { type: 'application/zip' });
+        const url = URL.createObjectURL(blob);
+        const a = document.createElement('a');
+        a.href = url;
+        a.download = (name || 'projekti').replace(/[^a-z0-9_-]/gi, '_') + '.zip';
+        a.click();
+        URL.revokeObjectURL(url);
+    };
+
+    // CRC-32 (ZIP-standardin mukainen)
+    const crc32Table = new Uint32Array(256);
+    for (let i = 0; i < 256; i++) {
+        let c = i;
+        for (let j = 0; j < 8; j++) c = (c & 1) ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1);
+        crc32Table[i] = c;
+    }
+    function crc32(data) {
+        let crc = 0xFFFFFFFF;
+        for (let i = 0; i < data.length; i++) crc = crc32Table[(crc ^ data[i]) & 0xFF] ^ (crc >>> 8);
+        return (crc ^ 0xFFFFFFFF) >>> 0;
+    }
+
     window.switchProjTab = function(id,i) {
         document.querySelectorAll(`.project-tab[data-card="${id}"]`).forEach((t,j) => t.classList.toggle('active', j===i));
         document.querySelectorAll(`.proj-panel[data-card="${id}"]`).forEach((p,j) => p.style.display = j===i ? '' : 'none');