docs(protocol): complete v2 migration docs and tests (step 9)

[arkanoider]

###Summary
Closes protocol v2 step 9: documentation polish for dual-transport protocol DMs and two unit tests. No runtime behavior changes. Follows #91; completes the migration plan.

Changes
docs/DM_LISTENER_FLOW.md — dual-transport table + mermaid; unwrap_incoming fix; manual verification checklist
docs/README.md + README.md — v2 complete wording; auto-select transport; pow_first_contact note
src/util/filters.rs — v1 filter shape test (kind 1059, no authors)
src/util/mostro_info.rs — is_v2_first_contact_protocol_action test

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 5d56a572-8adb-4acb-a364-dbbc6e43d168

📥 Commits

Reviewing files that changed from the base of the PR and between cdc0cb1 and 993556e.

📒 Files selected for processing (5)

• README.md
• docs/DM_LISTENER_FLOW.md
• docs/README.md
• src/util/filters.rs
• src/util/mostro_info.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/protocol-v2-tests-docs-step9

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[mostronatorcoder]

I did a pass on this PR and I do not see a blocker here.

This looks like the right kind of finishing slice for step 9:

• docs updated to describe the final dual-transport state more explicitly
• the added filter test usefully locks in the important v1 invariant that GiftWrap subscriptions must not constrain authors
• the added first-contact action test also helps prevent accidental widening/narrowing of the v2 PoW rule later

So from my side this is a good docs/tests follow-up and I do not see any correctness concern in the changes shown here.

[ermeme]

Code Review Summary

Verdict: Approve

Docs and tests look consistent with the current transport behavior. The new coverage checks the v1 filter shape and the v2 first-contact action gate, and the docs now match the implemented dual-transport flow.