Consume NIP-19 relay hints for event fetching

Extract and use relay hints from bech32 entities (nevent, nprofile, naddr)
and event tag references (e, q tags) to fetch events from hinted relays
not in the user's relay pool.

Changes:
- Parse relay hints from bech32 TLV data in URLHandler
- Pass relay hints through SearchType and NoteReference enums
- Add ensureConnected() to RelayPool for ephemeral relay connections
- Implement ephemeral relay lease management with race condition protection
- Add repostTarget() helper to extract relay hints from repost e tags
- Add QuoteRef struct to preserve relay hints from q tags (NIP-10/NIP-18)
- Support relay hints in replies with author pubkey in e-tags (NIP-10)
- Implement fallback broadcast when hinted relays don't respond
- Add comprehensive test coverage for relay hint functionality
- Add DEBUG logging for relay hint tracing during development

Implementation details:
- Connect to hinted relays as ephemeral, returning early when first connects
- Use total deadline to prevent timeout accumulation across hint attempts
- Decrement lease count before suspension points to ensure atomicity
- Fall back to broadcast if hints don't resolve or respond

Closes: https://github.com/damus-io/damus/issues/1147
Changelog-Added: Added relay hint support for nevent, nprofile, naddr links and event tag references (reposts, quotes, replies)
Signed-off-by: alltheseas
Signed-off-by: Daniel D'Aquino <daniel@daquino.me>
Co-authored-by: alltheseas <alltheseas@users.noreply.github.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: Daniel D'Aquino <daniel@daquino.me

nostrdb/NdbNote+.swift

@@ -32,4 +32,26 @@ extension NdbNote {
         }
         return self.parse_inner_event()
     }
+
+    /// Returns the target event ID and relay hints for a repost (kind 6) event.
+    ///
+    /// Per NIP-18, reposts MUST include an `e` tag with the reposted event's ID,
+    /// and the tag MUST include a relay URL as its third entry.
+    ///
+    /// - Returns: A tuple of (noteId, relayHints) if this is a repost with a valid e tag, nil otherwise.
+    func repostTarget() -> (noteId: NoteId, relayHints: [RelayURL])? {
+        guard self.known_kind == .boost else { return nil }
+
+        for tag in self.tags {
+            guard tag.count >= 2 else { continue }
+            guard tag[0].matches_char("e") else { continue }
+            guard let noteIdData = tag[1].id() else { continue }
+
+            let noteId = NoteId(noteIdData)
+            let relayHints = tag.relayHints
+            return (noteId, relayHints)
+        }
+
+        return nil
+    }
 }

nostrdb/NdbNote.swift

@@ -435,6 +435,10 @@ extension NdbNote {
         References<QuoteId>(tags: self.tags)
     }
 
+    public var referenced_quote_refs: References<QuoteRef> {
+        References<QuoteRef>(tags: self.tags)
+    }
+
     public var referenced_noterefs: References<NoteRef> {
         References<NoteRef>(tags: self.tags)
     }
@@ -539,6 +543,14 @@ extension NdbNote {
         return thread_reply()?.reply.note_id
     }
 
+    /// Returns the direct reply reference with relay hint if available.
+    ///
+    /// Per NIP-10, the reply `e` tag may include a relay URL at position 2 where
+    /// the replied-to event can be found.
+    public func direct_reply_ref() -> NoteRef? {
+        return thread_reply()?.reply
+    }
+
     // NDBTODO: just use Id
     public func thread_id() -> NoteId {
         guard let root = self.thread_reply()?.root else {

nostrdb/NdbTagIterator.swift

@@ -42,6 +42,36 @@ struct TagSequence: Sequence {
     }
 }
 
+// MARK: - Relay Hint Extraction
+
+extension TagSequence {
+    /// Extracts a relay URL hint from position 2 of the tag, if present and valid.
+    ///
+    /// Per NIP-01 and NIP-10, position 2 in `e`, `p`, `a`, and `q` tags contains an optional
+    /// relay URL where the referenced entity may be found.
+    ///
+    /// Example tag: `["e", "<event-id>", "wss://relay.example.com"]`
+    ///
+    /// - Returns: A valid `RelayURL` if position 2 contains a non-empty, valid relay URL; `nil` otherwise.
+    var relayHint: RelayURL? {
+        guard count >= 3 else { return nil }
+        let urlString = self[2].string()
+        guard !urlString.isEmpty else { return nil }
+        return RelayURL(urlString)
+    }
+
+    /// Extracts relay hints from the tag as an array.
+    ///
+    /// Currently tags only support a single relay hint at position 2, but this method
+    /// returns an array for consistency with `NEvent.relays` and future extensibility.
+    ///
+    /// - Returns: An array containing the relay hint if present, or an empty array.
+    var relayHints: [RelayURL] {
+        guard let hint = relayHint else { return [] }
+        return [hint]
+    }
+}
+
 struct TagIterator: IteratorProtocol {
     typealias Element = NdbTagElem