Support multiple named exports globally

Add multi-root bundle support across the toolchain:
 - `compile`: Accept multiple definition names via `-x NAME` (repeatable or
   comma-separated). Exports all requested definitions as named roots in a
   single bundle. Defaults to "main" when no names are given.
 - `export`: Accept comma-separated hashes in the positional argument and
   multiple `-n`/`names` flags. Exports all resolved roots in one bundle.
 - Server: Add `GET /bundle/roots?n=...&h=...` endpoint that resolves
   multiple stored-term names and/or raw Merkle hashes, returning a single
   bundle containing all of them as roots.
 - Wire: Export `defaultExportNames` helper for generating default export
   names when none are supplied.
 - Drop `cereal` dependency from `tricu.cabal` (no longer used).

src/Wire.hs

@@ -17,6 +17,7 @@ module Wire
   , exportBundle
   , exportNamedBundle
   , importBundle
+  , defaultExportNames
   ) where
 
 import ContentStore (getNodeMerkle, loadTree, putMerkleNode, storeTerm)