docs(readme): drop outdated TODO — sentrix-proto crate in use

[satyakwok]

Why

`crates/chain/proto/` vendored `.proto` was retired when `sentrix-proto 0.1.1` landed on crates.io (sentrix-labs/sentrix#667 + #670). `Cargo.toml` already pins `sentrix-proto = "0.1.1"`; the README directory tree still mentioned the vendored path with a TODO.

What

• `README.md:38` — drop "vendored — TODO swap for sentrix-proto crate from crates.io" — replace with one-liner saying `crates/chain/` wraps the crate

Test plan

• `grep -nr 'sentrix-proto' Cargo.toml crates/` shows the dependency in use
• No remaining "vendored" / "TODO swap" hits in README

Summary by CodeRabbit

• Documentation
  • Updated workspace documentation to clarify crate layout and organizational structure.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

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Run ID: dbd4b080-fef9-400a-b80a-e154b556e96b

📥 Commits

Reviewing files that changed from the base of the PR and between 657c2ae and f0eb51d.

📒 Files selected for processing (1)

• README.md

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📝 Walkthrough

Walkthrough

This PR updates README.md to clarify that crates/chain/ functions as a gRPC client wrapper around the upstream sentrix-proto crate. The change replaces a prior documentation entry that referenced a vendored sentrix.proto file under crates/chain/proto/ along with a TODO to migrate to the external crate. The update aligns the documentation with the current architecture.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related PRs

• Sentriscloud/indexer-rs#28: Both PRs update README.md's workspace layout documentation to document the location and handling of sentrix.proto within the crates/chain/ structure.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Description check	❓ Inconclusive	The description explains the 'why' and 'what' of the changes, but it doesn't fully follow the repository's PR template structure.	While the description is clear and purposeful, it deviates from the template by omitting standard sections like Scope, Checks, and Deploy impact. Consider using the full template structure for consistency with repository standards.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: removing an outdated TODO about the sentrix-proto crate from the README documentation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/staleness-fix-2026-05-14

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