chat: CESimplexNameUnprepared for found-but-no-link cases + member-removed filter

connectPlanName previously threw CEInvalidConnReq when a name lookup
hit a contact / group row whose preparedContact / preparedGroup was
NULL. The error message ("Connection link is invalid, possibly it was
created in a previous version") was wrong: the name resolved fine,
the device just has no link material to reconnect via (typical for a
contact created via the XInfo handler rather than the prepare path).
Introduce CESimplexNameUnprepared SimplexNameInfo for this case.

Also mirror the link-based path's gPlan (Commands.hs:4133) for groups
whose membership state is GSMemRemoved — return CESimplexNameNotFound
rather than GLPKnown for a removed-member group, since GLPKnown for
removed members would be inconsistent with how /_connect plan over a
short link handles the same situation.

src/Simplex/Chat/Controller.hs

@@ -1369,6 +1369,7 @@ data ChatErrorType
   | CEChatStoreChanged
   | CEInvalidConnReq
   | CESimplexNameNotFound {simplexName :: SimplexNameInfo}
+  | CESimplexNameUnprepared {simplexName :: SimplexNameInfo}
   | CEUnsupportedConnReq
   | CEInvalidChatMessage {connection :: Connection, msgMeta :: Maybe MsgMetaJSON, messageData :: Text, message :: String}
   | CEConnReqMessageProhibited