docs(api-reference): fix the one fabricated RPC method

Verified all 144 documented RPC methods against the dispatcher. 143 are live;
one was fabricated: `mesh.discover` (params { timeout_secs? }, returns
{ nodes: MeshNode[] }) does not exist — "mesh discovery" appears only in code
comments as a concept, never as a method. A developer calling it gets "unknown
method".

Replaced with the real peer-listing method `mesh.peers` (no params, returns
{ peers, count }), which the frontend actually uses and which was undocumented.

Also verified: every source path cited across the docs resolves (placeholders
and a correctly-recorded deletion aside), and every documented app-manifest
field exists in the schema (no fabricated fields).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/api-reference.md

@@ -263,7 +263,7 @@ All endpoints use JSON-RPC over HTTP POST to `/rpc/v1`.
 | Method | Params | Returns | Auth |
 |--------|--------|---------|------|
 | `mesh.status` | — | `{ enabled: bool, device: string?, nodes: MeshNode[] }` | Yes |
-| `mesh.discover` | `{ timeout_secs?: number }` | `{ nodes: MeshNode[] }` | Yes |
+| `mesh.peers` | — | `{ peers: MeshPeer[], count: number }` | Yes |
 | `mesh.broadcast` | — | `{ ok: bool }` | Yes |
 | `mesh.configure` | `{ enabled: bool, device?: string }` | `{ ok: bool }` | Yes |