doc: update stale tooling references

[zhanzhao-h]

Description

Updates stale tooling references in the macOS build and release process documentation.

The docs now point to the current GitHub repository URLs and Bitgesell release naming instead of inherited Bitcoin Core references.

Notes

Docs-only change.

BTC/BGL PR reward address

To be provided if applicable.

Validation:

• git diff --check origin/master..doc/fix-stale-tooling-refs
• rg -n "bitcoin-core/gui|bitcoin-core/packaging|bitcoin-[0-9]|SHA256SUMS.asc" doc/build-osx.md doc/release-process.md

Refs #32

[MyTH-zyxeon]

Maintainer review note for the #32/#81 bounty queue:

This docs-only cleanup is mostly aligned with the current tree. I checked head 098ac8a: contrib/install_db4.sh is not present, so removing the old local-script fallback from doc/build-osx.md matches the repository state, and src/secp256k1/tools/check-abi.sh exists for the release-process retarget.

One small acceptance check before merge: doc/build-osx.md now says berkeley-db@4 in the explanatory text but the install command is brew install berkeley-db4. If both names are intentionally supported by the selected Homebrew tap, this is fine; otherwise I would normalize the text/command pair so a fresh macOS builder does not copy a stale formula name.

Scope looks safe if kept to docs-only retargeting: no build logic, wallet/key material, node/RPC, dependency installation, or live-chain behavior changes are introduced by this PR.

[MikeGarciaAGM]

Looks good. The tooling references are updated cleanly and the docs-only scope is nice and narrow.