Replace legacy scripts with separated ots/node hooks

- Remove deprecated scripts/ directory (6 files)
- Add hooks/post-commit-ots (ots CLI version)
- Add hooks/pre-commit-ots (ots CLI backfill)
- Add hooks/post-commit-node (Node.js version, local proofs only)
- Add hooks/pre-commit-node (Node.js backfill, no upgrade)
- Update hooks/install.sh to auto-detect and install matching hooks
- Update documentation (SKILL.md, README.md, AGENTS.md)
- Add node_modules/ to .gitignore for Node.js mode

Breaking change: Scripts removed, use new hooks/ directory.

hooks/post-commit-node

@@ -0,0 +1,49 @@
+#!/bin/bash
+# Git OpenTimestamp Post-Commit Hook (Node.js version)
+# Requires: @opentimestamps/ots (npm install)
+
+set -e
+
+OUTPUT_DIR=".ots"
+OUTPUT_FILE="$OUTPUT_DIR/proof.ots"
+
+mkdir -p "$OUTPUT_DIR"
+
+COMMIT_HASH=$(git rev-parse HEAD)
+
+# Generate proof using Node.js
+node -e "
+const ots = require('@opentimestamps/ots');
+const fs = require('fs');
+const hash = '$COMMIT_HASH';
+const output = '$OUTPUT_FILE';
+const hashBuffer = Buffer.from(hash, 'hex');
+
+ots.Timestamp.hash(hashBuffer).then(timestamp => {
+    // Note: This creates a local proof only, not submitted to calendars
+    // For full Bitcoin attestation, use the ots CLI version
+    const proof = {
+        hash: hash,
+        timestamp: new Date().toISOString(),
+        status: 'pending',
+        note: 'Local proof only - use ots CLI for calendar submission'
+    };
+    fs.writeFileSync(output, JSON.stringify(proof, null, 2));
+    console.log('[ots-node] Generated local proof: ' + hash.substring(0, 8));
+}).catch(err => {
+    console.error('[ots-node] Error:', err.message);
+    process.exit(1);
+});
+"
+
+# Save previous commit for chaining
+PREV_COMMIT=$(git rev-parse HEAD^1 2>/dev/null || echo "")
+if [ -n "$PREV_COMMIT" ]; then
+    echo "$PREV_COMMIT" > "$OUTPUT_DIR/prev-commit.txt"
+fi
+
+# Create individual proof file (JSON format for node version)
+INDIVIDUAL_PROOF="$OUTPUT_DIR/${COMMIT_HASH}.ots"
+cp "$OUTPUT_FILE" "$INDIVIDUAL_PROOF"
+
+echo "[ots-node] Proof generated successfully"