docs: clarify public-api warning behavior

[UfukNode]

Summary

• clarify that --public-api enforces pending-transaction hiding, but does not rewrite or reject --http.api / --ws.api selections
• make it explicit that unsafe namespace selections only produce a startup warning and the node continues to serve those namespaces
• remind operators that public endpoints must still be configured with only the safe RPC namespaces

Why

The previous wording said --public-api enforced the public RPC restrictions at runtime. In code, unsafe namespace selections only trigger warn_if_public_api_unsafe, so the docs could imply stronger protection than the node actually applies.

Relevant code:

• https://github.com/circlefin/arc-node/blob/main/crates/node/src/main.rs#L426-L436
• https://github.com/circlefin/arc-node/blob/main/crates/node/src/main.rs#L578-L582

Testing

• git diff --check

[osr21]

Assessment

The PR is correct and the fix matters. Worth expanding on why the distinction is security-relevant for node operators.

What --public-api actually enforces

The flag does two distinct things:

Behaviour	Enforced?
Hide pending-tx RPCs (txpool_*, etc.)	✅ Yes — actively blocked at runtime
Strip unsafe namespaces from --http.api / --ws.api	❌ No — startup warning only, non-fatal

The old wording ("enforces these restrictions at runtime") implied the second row was also active enforcement. An operator who reads that, adds --public-api, and forgets to audit --http.api could expose debug / trace / admin while believing the flag protected them.

Consistency with the rest of the doc

The intro section (~line 400 of the current main branch) already uses "warns if --http.api / --ws.api exposes namespaces beyond the safe set" — so this PR also fixes an internal inconsistency.

Suggestions

1. State the non-fatal consequence explicitly. The new text says "warns at startup" but a reader could still wonder whether the node refuses to start. A short addition like "…warns at startup (the node continues to start and serve those namespaces regardless)" removes all ambiguity.

2. Cite the source location. The PR description says "In code, unsafe namespace selections only trigger a startup warning." Linking to or quoting the relevant function would make this self-verifying for future reviewers and prevent the same misunderstanding from creeping back in.

3. Consider a callout block. Operators skimming the doc are the audience this protects. A > ⚠️ Note: callout makes the "you must still configure --http.api correctly" point harder to miss than inline prose.

Overall: merge-worthy as-is. The factual correction is important and the new wording is clearer. The suggestions above are optional improvements, not blockers.