feat: add hostname substitution in user@host patterns

jsmith@macbook-pro now becomes ademo@mycomputer when both username
and hostname are configured in the Identity tab. Hostnames are also
caught standalone (e.g. just "macbook-pro" in text).

Also rewrites README with detailed step-by-step Mozilla API key
setup instructions for Firefox signing.

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

src/content/content.js

@@ -186,15 +186,22 @@
       }
     }
 
-    // Usernames + paths
+    // Usernames + hostnames + paths
     if (id.enabled.usernames !== false) {
+      const hostMap = new Map();
+      for (const h of (id.hostnames || [])) {
+        if (h.real && h.substitute) hostMap.set(h.real.toLowerCase(), h);
+      }
+
       for (const u of (id.usernames || [])) {
         if (!u.real || !u.substitute) continue;
 
-        // user@hostname
+        // user@hostname (substitute both username and hostname if configured)
         result = result.replace(new RegExp(esc(u.real) + '@[a-zA-Z0-9._\\-]+', 'g'), (matched) => {
           const host = matched.slice(u.real.length + 1);
-          const sub = u.substitute + '@' + host;
+          const hostEntry = hostMap.get(host.toLowerCase());
+          const subHost = hostEntry ? hostEntry.substitute : host;
+          const sub = u.substitute + '@' + subHost;
           replacements.push({ original: matched, replaced: sub, category: 'username', pattern: 'smart' });
           return sub;
         });
@@ -228,6 +235,16 @@
           });
         }
       }
+
+      // Standalone hostname substitution
+      for (const [, h] of hostMap) {
+        if (h.real.length >= 3) {
+          result = result.replace(new RegExp('\\b' + esc(h.real) + '\\b', 'gi'), (matched) => {
+            replacements.push({ original: matched, replaced: h.substitute, category: 'hostname', pattern: 'smart' });
+            return h.substitute;
+          });
+        }
+      }
     }
 
     return { text: result, replacements };

src/lib/smart-patterns.js

@@ -222,13 +222,17 @@ const SmartPatterns = {
     return { text: result, replacements };
   },
 
-  // ----- Usernames -----
+  // ----- Usernames + Hostnames -----
   // Catches: user@hostname, ~username, /home/username, mentions of username
-  // in shell/code contexts
+  // in shell/code contexts. Also substitutes hostnames independently.
   _substituteUsernames(text, identity) {
     const replacements = [];
     let result = text;
     const usernames = identity.usernames || [];
+    const hostMap = new Map();
+    for (const h of (identity.hostnames || [])) {
+      if (h.real && h.substitute) hostMap.set(h.real.toLowerCase(), h);
+    }
 
     for (const u of usernames) {
       if (!u.real || !u.substitute) continue;
@@ -240,7 +244,10 @@ const SmartPatterns = {
       );
       result = result.replace(userHostRegex, (matched) => {
         const host = matched.slice(u.real.length + 1);
-        const sub = u.substitute + '@' + host;
+        // Also substitute hostname if configured
+        const hostEntry = hostMap.get(host.toLowerCase());
+        const subHost = hostEntry ? hostEntry.substitute : host;
+        const sub = u.substitute + '@' + subHost;
         replacements.push({
           original: matched,
           replaced: sub,
@@ -279,6 +286,22 @@ const SmartPatterns = {
       }
     }
 
+    // Standalone hostname substitution (catches hostnames appearing on their own)
+    for (const [, h] of hostMap) {
+      if (h.real.length >= 3) {
+        const hostRegex = new RegExp('\\b' + esc(h.real) + '\\b', 'gi');
+        result = result.replace(hostRegex, (matched) => {
+          replacements.push({
+            original: matched,
+            replaced: h.substitute,
+            category: 'hostname',
+            pattern: 'smart-hostname',
+          });
+          return h.substitute;
+        });
+      }
+    }
+
     return { text: result, replacements };
   },
 

src/popup/popup.html

@@ -74,7 +74,12 @@
           <span class="arrow">&rarr;</span>
           <input type="text" id="idUserSub" placeholder="ademo" class="input input-sm">
         </div>
-        <div class="id-hint">Catches: jsmith@hostname, /home/jsmith, ~jsmith, C:\Users\jsmith</div>
+        <div class="id-row">
+          <input type="text" id="idHostReal" placeholder="macbook-pro" class="input input-sm">
+          <span class="arrow">&rarr;</span>
+          <input type="text" id="idHostSub" placeholder="mycomputer" class="input input-sm">
+        </div>
+        <div class="id-hint">Catches: jsmith@macbook-pro, /home/jsmith, ~jsmith, C:\Users\jsmith</div>
       </div>
 
       <div class="id-section">

src/popup/popup.js

@@ -111,6 +111,11 @@ function loadIdentityForm() {
     $('#idUserReal').value = user.real || '';
     $('#idUserSub').value = user.substitute || '';
   }
+  const host = (identity.hostnames || [])[0];
+  if (host) {
+    $('#idHostReal').value = host.real || '';
+    $('#idHostSub').value = host.substitute || '';
+  }
   if (phone) {
     $('#idPhoneReal').value = phone.real || '';
     $('#idPhoneSub').value = phone.substitute || '';
@@ -144,6 +149,13 @@ async function saveIdentity() {
     usernames.push({ real: userReal, substitute: userSub });
   }
 
+  const hostnames = [];
+  const hostReal = $('#idHostReal').value.trim();
+  const hostSub = $('#idHostSub').value.trim();
+  if (hostReal && hostSub) {
+    hostnames.push({ real: hostReal, substitute: hostSub });
+  }
+
   const phones = [];
   const phoneReal = $('#idPhoneReal').value.trim();
   const phoneSub = $('#idPhoneSub').value.trim();
@@ -155,6 +167,7 @@ async function saveIdentity() {
     names,
     emails,
     usernames,
+    hostnames,
     phones,
     catchAllEmail: $('#idCatchAllEmail').value.trim(),
     emailDomains: identity.emailDomains || [],