Add feed aggregation from enabled relays

- src/feed.rs: aggregate recent kind 1 notes from enabled relays into a
  newest-first, de-duplicated feed using a throwaway identity
- IPC: FeedGet; CLI: feed [limit]; frontend: Feed screen + nav + tests
- README: mark feed aggregation as shipped

README.md

@@ -45,7 +45,8 @@ distribution repositories. Expect some API churn until 1.0. No Docker or databas
   - **Link preview cards** — up to three URLs per note get a title/image/description preview
 - **Publishing receipts** — per-relay publish reports, so you always know where a note landed
 - **Relay management** — add, remove, enable/disable, and latency-test relays from GUI or CLI
-  - **Feed aggregation** *(coming soon)* — an aggregated view of incoming text notes and link cards
+  - **Feed aggregation** — a read-only, newest-first feed of recent text notes aggregated from your
+    enabled relays (24h window), de-duplicated across relays, from a dedicated GUI screen or the CLI
 - **Encrypted vault** — secret keys encrypted at rest with **AES-256-GCM** under a key derived via
   **Argon2id** from your password
 - **Secret key recovery** — reveal a key (hex + `nsec1...`) only after unlocking, from GUI or CLI
@@ -210,6 +211,7 @@ cargo run --release -- create "Alice"            # create a profile
 cargo run --release -- list                      # list profiles (no secret keys)
 cargo run --release -- switch <npub>             # select the active profile
 cargo run --release -- publish <npub> "Hello"    # publish a text note
+cargo run --release -- feed [limit]              # fetch recent notes from enabled relays
 cargo run --release -- relays list|add|remove|enable|disable|test
 cargo run --release -- settings get|set <key> <value>
 cargo run --release -- set-password              # encrypt the vault (or change its password)