Add yaw2 invite interoperability

Protocol:
- invite.go: include full 64-char `net` hash in waste: invite blob
  (matches yaw2's `net` field — any client parsing the base64 JSON can
  join without knowing the plaintext name). Expose NetHash() helper.
- netmgr: add JoinByHash() — join via full 64-char hex hash alone,
  storing the short ID as display name. Enables joining yaw2 networks
  from a URL that only carries the hash.
- anchor: expose RunByHash() so netmgr can pass a pre-computed hash
  directly without a name→hash roundtrip.
- ipc/proto: add network_hash field to join_network — routes to
  JoinByHash when present and network_name is absent.

Web UI:
- Parse ?net=<64hex> (yaw2 URL param) and ?a=<anchor> in addition to
  existing ?n= / ?invite= params. Hash-only joins send network_hash.
- Sidebar shows yaw: contact card (yaw:<masterID>?n=<alias>) using the
  master identity — compatible with yaw2 contact card format. Click to
  copy to clipboard.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/proto/proto.go

@@ -265,7 +265,8 @@ type IpcMessage struct {
 
 	// join_network / leave_network
 	NetworkName string `json:"network_name,omitempty"`
-	ShareDir    string `json:"share_dir,omitempty"` // optional per-network share directory
+	NetworkHash string `json:"network_hash,omitempty"` // 64-char hex (yaw2 `net` field); alternative to network_name
+	ShareDir    string `json:"share_dir,omitempty"`    // optional per-network share directory
 
 	// send_file / set_share_dir / file_complete path
 	Path string `json:"path,omitempty"`