feat(p2p): log the resolved iroh relay set at endpoint spawn

[jackzampolin]

Why

Follow-up to the defra-agent#588 incident (relay open_path flood against unreachable n0 canary relays). During the incident nothing in the logs showed which relay infrastructure the endpoint was pointed at — canary vs production was invisible at default verbosity.

What

Slimmed down after #1084 merged (which landed the iroh 1.0.1 / gossip 0.101 / blobs 0.103 / tickets 1.0.0 bump this PR originally carried — thanks!). What remains is the observability piece: log the resolved relay URL set once at spawn_endpoint in crates/p2p/src/iroh/endpoint.rs, so every deployment shows its relay infrastructure at startup.

Verification

• cargo check -p p2p --all-features green on top of chore(deps): update Iroh to final 1.0 release #1084
• cargo fmt --check green

The fix/iroh-1.0-on-v0.15.1 branch mentioned earlier is now obsolete (defra-agent pins the #1084 merge rev directly) — I'll delete it.

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📥 Commits

Reviewing files that changed from the base of the PR and between 407985f and df9299c.

📒 Files selected for processing (1)

• crates/p2p/src/iroh/endpoint.rs

✅ Files skipped from review due to trivial changes (1)

• crates/p2p/src/iroh/endpoint.rs

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⏰ Context from checks skipped due to timeout. (1)

• GitHub Check: Build & Test

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📝 Walkthrough

Walkthrough

In spawn_endpoint, relay URLs derived from relay_mode are collected into a Vec<String> and logged via tracing::info! before the iroh endpoint is built and bound. No other logic changes were made.

Changes

Relay Logging

Layer / File(s)	Summary
Relay configuration logging crates/p2p/src/iroh/endpoint.rs	Relay URLs from relay_mode are collected into a Vec<String> and logged via tracing::info! prior to building/binding the endpoint.

Estimated code review effort: 1 (Trivial) | ~2 minutes

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[jackzampolin]

Also pushed fix/iroh-1.0-on-v0.15.1 (= v0.15.1 + this commit cherry-picked, fca7c36) so defra-agent can rev-pin the incident fix without absorbing unrelated main drift; defra-agent will switch to the next tag once this merges. Feel free to delete that branch after a v0.15.3 (or equivalent) tag exists.