docs(README): update stale base-org references to base after org rename

[0xAxiom]

Closes #248.

The GitHub organization was renamed from base-org to base. The old base-org/* URLs still redirect, but the README still surfaces them in two places:

1. The Markdown link to the contract-deployments repo on line 7.
2. The img.shields.io badge source URLs in lines 11–15 and 27–28. (The rendered badge target links already point at base/* and were left unchanged.)

This PR updates both to use the canonical base/* paths.

Diff summary

• 1 file changed, 8 insertions(+), 8 deletions(-)
• README-only, no contract or build changes.

[cb-heimdall]

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