fix(register.sh): handle space after colon in JSON response for builder_code

[erhnysr]

Problem

Fixes #54.

The grep pattern on line 21 of register.sh requires no space between : and " in the JSON response:

# Old — fails on spaced JSON ("builder_code": "bc_...")
BUILDER_CODE=$(echo "$RESPONSE" | grep -o '"builder_code":"[^"]*"' | cut -d'"' -f4)

However, the reference doc (references/agents/register.md) shows the API response with a space after the colon. When the API returns spaced JSON, BUILDER_CODE is empty and the script exits 1 — registration silently fails.

Fix

Use a space-tolerant grep pattern (no new dependencies):

# New — handles both compact and spaced JSON
BUILDER_CODE=$(echo "$RESPONSE" | grep -o '"builder_code": *"[^"]*"' | grep -o '"[^"]*"$' | tr -d '"')

Verification

# Spaced (as shown in reference doc) — now works
echo '{"builder_code": "bc_a1b2c3d4","wallet_address":"0x123"}' | grep -o '"builder_code": *"[^"]*"' | grep -o '"[^"]*"$' | tr -d '"'
# → bc_a1b2c3d4

# Compact — still works
echo '{"builder_code":"bc_a1b2c3d4","wallet_address":"0x123"}' | grep -o '"builder_code": *"[^"]*"' | grep -o '"[^"]*"$' | tr -d '"'
# → bc_a1b2c3d4

[cb-heimdall]

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