Turn @usernames into Discourse user mentions/links

No notifications are sent for appearing in a journal, but profile
popovers etc. all work like mentions anywhere else in a topic.

test/javascripts/acceptance/hledger-test.js

@@ -49,6 +49,23 @@ const accountsReport = {
             { commodity: "EUR", quantity: "-1000.0", display: "(1000.00 EUR)" },
           ],
         },
+        {
+          account: "equity:members:@tony",
+          label: "@tony",
+          depth: 2,
+          root: false,
+          mention: { username: "tony", text: "@tony" },
+          amounts: [
+            { commodity: "EUR", quantity: "-1000.0", display: "(1000.00 EUR)" },
+          ],
+        },
+        {
+          account: "equity:members:@nobody",
+          label: "@nobody",
+          depth: 2,
+          root: false,
+          amounts: [{ commodity: "EUR", quantity: "0.0", display: "0.00 EUR" }],
+        },
       ],
       total: [{ commodity: "EUR", quantity: "1000.0", display: "1000.00 EUR" }],
     },
@@ -203,6 +220,17 @@ const transactionsReport = {
             { commodity: "EUR", quantity: "-400.0", display: "-400.00 EUR" },
           ],
         },
+        {
+          account: "equity:members:@tony",
+          account_segments: [
+            { text: "equity" },
+            { text: "members" },
+            { text: "@tony", username: "tony" },
+          ],
+          amounts: [
+            { commodity: "EUR", quantity: "-600.0", display: "-600.00 EUR" },
+          ],
+        },
       ],
     },
     {
@@ -296,6 +324,15 @@ acceptance("Hledger plugin", function (needs) {
     assert
       .dom('.hledger-dashboard__account[title="assets:bank"]')
       .hasText("Bank");
+    assert
+      .dom('a.mention[href="/u/tony"][data-user-card="tony"]')
+      .hasText("@tony", "links a mentioned account to its user");
+    assert
+      .dom('.hledger-dashboard__account[title="equity:members:@nobody"] a')
+      .doesNotExist("leaves an unknown mention as plain text");
+    assert
+      .dom('.hledger-dashboard__account[title="equity:members:@nobody"]')
+      .hasText("@nobody");
 
     const rootAccount = document.querySelector(
       ".hledger-dashboard__account.--depth-0"
@@ -437,5 +474,11 @@ acceptance("Hledger plugin", function (needs) {
       .dom(".hledger-dashboard__table")
       .includesText("assets:bank:checking");
     assert.dom(".hledger-dashboard__table").includesText("1000.00 EUR");
+    assert
+      .dom(".hledger-dashboard__table")
+      .includesText("equity:members:@tony", "keeps path separators");
+    assert
+      .dom('a.mention[href="/u/tony"][data-user-card="tony"]')
+      .hasText("@tony", "links a mentioned account in the journal");
   });
 });