feat: browse your own shares as a peer receives them

The window could show any peer's share tree but never this account's, so
"am I actually sharing that?" had no answer short of asking a friend to
browse you. The tree is already there; what was missing was feeding it
from our own index.

B opens it — the same collapsible tree, filter, and navigation the peer
browse offers, built from `Shares::directories()`, which is the listing
GetShareFileList answers with. So what it shows is what the network sees,
not what the config meant to share. r re-scans the disk rather than
re-asking a peer, o steps across to the folders that feed it, and nothing
here queues a download from ourselves.

Attached to a daemon the index lives on the daemon's host, so it comes
back over a new `shares.files` method rather than being scanned locally;
`shares files [--filter]` prints the same listing headless, through the
`emit_listing` that `browse` now shares with it — the two are only
comparable while they are built the same way.

Two allocation fixes came out of the review, both on paths this reaches:
the daemon hands its listing to the DTO instead of deep-copying one it
already owns, and `Shares::directories()` allocates its map key once per
folder rather than once per file, which the peer-facing serve path has
been paying for all along.

soulseek-rs/src/api.rs

@@ -168,6 +168,10 @@ pub trait SessionApi: Send + Sync {
     fn shared_counts(&self) -> (u32, u32);
     // aislop-ignore-next-line complexity/function-too-long -- same scanner bug: bodyless signature measured to EOF. One line.
     fn shared_directories(&self) -> Vec<String>;
+    /// The share index in the shape a peer receives it, for showing this
+    /// session's own files exactly as the network sees them.
+    // aislop-ignore-next-line complexity/function-too-long -- same scanner bug: bodyless signature measured to EOF. One line.
+    fn shared_listing(&self) -> Vec<SharedDirectory>;
     // aislop-ignore-next-line complexity/function-too-long -- same scanner bug: bodyless signature measured to EOF. One line.
     fn set_shared_directories(&self, directories: Vec<String>) -> Result<()>;
 
@@ -416,6 +420,10 @@ impl SessionApi for Client {
         Self::shared_directories(self)
     }
 
+    fn shared_listing(&self) -> Vec<SharedDirectory> {
+        Self::shared_listing(self)
+    }
+
     fn set_shared_directories(&self, directories: Vec<String>) -> Result<()> {
         Self::set_shared_directories(self, directories)
     }