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/docs/openrpc.json

@@ -1243,6 +1243,21 @@
         ],
         "type": "object"
       },
+      "SharedListing": {
+        "description": "This session's own share index, as a peer receives it — what\n`shares.files` answers with.",
+        "properties": {
+          "directories": {
+            "items": {
+              "$ref": "#/components/schemas/SharedDirectoryDto"
+            },
+            "type": "array"
+          }
+        },
+        "required": [
+          "directories"
+        ],
+        "type": "object"
+      },
       "SharesStatus": {
         "description": "What the share index holds, from `shares.status` / `shares.reindex`.",
         "properties": {
@@ -2361,6 +2376,18 @@
       },
       "summary": "What the share index currently holds."
     },
+    {
+      "name": "shares.files",
+      "paramStructure": "by-name",
+      "params": [],
+      "result": {
+        "name": "result",
+        "schema": {
+          "$ref": "#/components/schemas/SharedListing"
+        }
+      },
+      "summary": "Every indexed file, in the listing a browsing peer receives."
+    },
     {
       "name": "shares.set",
       "paramStructure": "by-name",