feat: identity lifecycle tests and ADR-011 DWN deprioritization

Added 8 integration tests for identity manager covering create,
sign/verify, list, delete, default management, and Nostr key gen.
Documented DWN deprioritization decision.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/adr/011-dwn-deprioritization.md

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+# ADR-011: DWN Deprioritization
+
+## Status
+
+Accepted
+
+## Context
+
+TBD/Block shut down in November 2024, donating Web5 code to the Decentralized Identity Foundation (DIF). The DWN (Decentralized Web Node) specification was heavily backed by TBD — without their engineering team, the spec has lost momentum:
+
+- No maintained Rust DWN SDK exists (the `dwn` crate by unavi-xyz is v0.4.0 with 323 downloads)
+- TBD's reference implementation was TypeScript-only
+- DIF has not allocated resources to continue DWN development
+- The spec itself is complex (personal data stores with protocol-based access control)
+
+Meanwhile, Archipelago's federation over Tor + Nostr relays already serves the core peer data sync use case that DWN was intended for.
+
+## Decision
+
+1. **Keep existing DWN store code** in `core/archipelago/src/network/dwn_store.rs` — it works for peer file catalogs and federation state
+2. **Stop calling it "Web5 DWN"** in user-facing text — it's our custom implementation, not a full DWN spec implementation
+3. **Do not invest in DWN spec compliance** — the spec is stalled and may not stabilize
+4. **Prioritize Nostr + federation** for peer discovery and data exchange
+5. **Re-evaluate if DIF produces a viable Rust SDK** or the spec gains new maintainers
+
+## Consequences
+
+- DWN functionality remains available but is not actively developed
+- Peer sync uses federation + Nostr instead of DWN protocols
+- Reduces maintenance burden — no need to track a stalled spec
+- If DWN resurfaces with strong tooling, we can adopt it later