fix(register.sh): handle pretty-printed JSON with space after colon

[Nexory]

Closes #54

This patch fixes the grep pattern in skills/build-on-base/scripts/register.sh line 21 so it tolerates the space-after-colon format that the API actually returns (as documented in references/agents/register.md).

Before:

BUILDER_CODE=$(echo "$RESPONSE" | grep -o '"builder_code":"[^"]*"' | cut -d'"' -f4)

The pattern requires no space between the colon and the value, so the pretty-printed format "builder_code": "bc_..." matches zero bytes, BUILDER_CODE becomes empty, and the script exits 1.

After:

BUILDER_CODE=$(echo "$RESPONSE" | grep -oE '"builder_code": *"[^"]*"' | grep -oE '"[^"]*"$' | tr -d '"')

The new pattern uses grep -E with a *-quantifier between the colon and the opening quote, matching zero or more spaces. A second grep -oE extracts the trailing quoted value, then tr -d '"' strips the quotes. No new dependencies (still pure POSIX). Both compact and pretty-printed JSON now work.

Reproduction confirming the fix:

# Spaced JSON (current API format)
echo '{"builder_code": "bc_a1b2c3d4"}' | grep -oE '"builder_code": *"[^"]*"' | grep -oE '"[^"]*"$' | tr -d '"'
# -> bc_a1b2c3d4 (PASS)

# Compact JSON (legacy)
echo '{"builder_code":"bc_a1b2c3d4"}' | grep -oE '"builder_code": *"[^"]*"' | grep -oE '"[^"]*"$' | tr -d '"'
# -> bc_a1b2c3d4 (PASS)

Both formats produce identical output, the original bug is gone, and no new dependency is introduced.

[cb-heimdall]

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