docs(readme): fix two stale claims (published box + explorer dep)

[satyakwok]

12 of N. Fixed: (1) Roadmap had Publish to crates.io as unchecked but v0.1.0-alpha.0 is live on crates.io since 2026-05-12. (2) Status claimed explorer-v2 depends on this crate — verified Cargo.toml shows it does NOT; both are sibling consumers of sentrix-proto. Reframed to capture the actual extraction lineage.

Summary by CodeRabbit

Documentation

• Updated README to reflect the publication of sentrix-grpc-wasm v0.1.0-alpha.0 on crates.io (dated 2026-05-12)
• Refreshed status section with current project information and updated roadmap items

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 4b539d2d-2863-4597-b626-d599ef69e61a

📥 Commits

Reviewing files that changed from the base of the PR and between 3b1d61d and 5f0ecd6.

📒 Files selected for processing (1)

• README.md

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📝 Walkthrough

Walkthrough

The README documentation was updated to reflect the release of sentrix-grpc-wasm as version v0.1.0-alpha.0 on crates.io (2026-05-12). The "Roadmap" section now marks this publication as complete and removes the stale "publish once API surface stabilises" item. The "Status" section was expanded to provide more context about the crate's origin as an extraction from sentrix-explorer-v2 and its relationship to sentrix-proto and the gRPC-Web glue.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main changes: updating two stale README claims about the crates.io publication status and the explorer dependency relationship.
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/polish-readme-truth

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