docs: fix remaining broken and outdated links from #1170

[kutluhaneth46]

Summary

#1173 already updates the reth pruning URLs in the env files. These three links from #1170 are still broken/outdated on main:

1. README.md — https://basechaindata.vercel.app (404) → Base snapshots docs
2. SECURITY.md — Optimism Bedrock docs URL (404) → current OP Stack getting-started page
3. CONTRIBUTING.md — old Coinbase support portal URL (redirect) → https://help.coinbase.com/en

Note: #1174 removes the [3] definition in CONTRIBUTING.md while the body still references [our support team][3]. This PR keeps the reference and updates the destination instead.

Test plan

• curl -I -L each new URL returns a successful final response
• Confirm old URLs still 404 / redirect as described in docs: broken and outdated links in README, SECURITY.md, CONTRIBUTING.md, and env files #1170

Fixes #1170

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[kutluhaneth46]

@danyalprout Noticed this was closed without merge — totally fine if it was intentional.

Quick status check against current main in case it helps: the three targets from #1170 still look broken/outdated on HEAD:

• SECURITY.md → https://docs.optimism.io/docs/releases/bedrock/ (404)
• CONTRIBUTING.md → old support.coinbase.com/... portal URL (dead)
• README.md still points snapshot sizing at basechaindata.vercel.app (the docs.base.org snapshots page is the live one)

Happy to reopen/refresh this PR if useful, or stand down if you'd rather handle it in-tree. Thanks either way!

[danyalprout]

@kutluhaneth46 we're in the process of archiving this repo (to move all dev and releases to base/base). If they're still issues there, feel free to open a PR and @ me on it and we'll merge.

[kutluhaneth46]

Thanks @danyalprout — checked base/base against the three #1170 leftovers:

• SECURITY.md — no more docs.optimism.io/docs/releases/bedrock/ link
• CONTRIBUTING.md — no more dead support.coinbase.com/.../portal/... URL
• README.md — snapshots point at docs.base.org (not basechaindata.vercel.app)

Looks like those are already fixed in the new repo, so I won’t open a duplicate PR there. Appreciate the pointer on the archive move.