feat: add email service with Nodemailer and 6 HTML templates

EmailService with mock fallback when SMTP not configured.
Templates: welcome, fiel-notification, payment-confirmed,
payment-failed, subscription-expiring, subscription-cancelled.
Uses Google Workspace SMTP (STARTTLS).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pnpm-lock.yaml

@@ -68,6 +68,9 @@ importers:
       node-forge:
         specifier: ^1.3.3
         version: 1.3.3
+      nodemailer:
+        specifier: ^8.0.2
+        version: 8.0.2
       pg:
         specifier: ^8.18.0
         version: 8.18.0
@@ -99,6 +102,9 @@ importers:
       '@types/node-forge':
         specifier: ^1.3.14
         version: 1.3.14
+      '@types/nodemailer':
+        specifier: ^7.0.11
+        version: 7.0.11
       '@types/pg':
         specifier: ^8.18.0
         version: 8.18.0
@@ -1109,6 +1115,9 @@ packages:
   '@types/node@22.19.7':
     resolution: {integrity: sha512-MciR4AKGHWl7xwxkBa6xUGxQJ4VBOmPTF7sL+iGzuahOFaO0jHCsuEfS80pan1ef4gWId1oWOweIhrDEYLuaOw==}
 
+  '@types/nodemailer@7.0.11':
+    resolution: {integrity: sha512-E+U4RzR2dKrx+u3N4DlsmLaDC6mMZOM/TPROxA0UAPiTgI0y4CEFBmZE+coGWTjakDriRsXG368lNk1u9Q0a2g==}
+
   '@types/pako@2.0.4':
     resolution: {integrity: sha512-VWDCbrLeVXJM9fihYodcLiIv0ku+AlOa/TQ1SvYOaBuyrSKgEcro95LJyIsJ4vSo6BXIxOKxiJAat04CmST9Fw==}
 
@@ -1961,6 +1970,10 @@ packages:
   node-releases@2.0.27:
     resolution: {integrity: sha512-nmh3lCkYZ3grZvqcCH+fjmQ7X+H0OeZgP40OierEaAptX4XofMh5kwNbWh7lBduUzCcV/8kZ+NDLCwm2iorIlA==}
 
+  nodemailer@8.0.2:
+    resolution: {integrity: sha512-zbj002pZAIkWQFxyAaqoxvn+zoIwRnS40hgjqTXudKOOJkiFFgBeNqjgD3/YCR12sZnrghWYBY+yP1ZucdDRpw==}
+    engines: {node: '>=6.0.0'}
+
   normalize-path@3.0.0:
     resolution: {integrity: sha512-6eZs5Ls3WtCisHWp9S2GUy8dqkpGi4BVSz3GaqiE6ezub0512ESztXUwUB6C6IKbQkY2Pnb/mD4WYojCRwcwLA==}
     engines: {node: '>=0.10.0'}
@@ -3376,6 +3389,10 @@ snapshots:
     dependencies:
       undici-types: 6.21.0
 
+  '@types/nodemailer@7.0.11':
+    dependencies:
+      '@types/node': 22.19.7
+
   '@types/pako@2.0.4': {}
 
   '@types/pg@8.18.0':
@@ -4277,6 +4294,8 @@ snapshots:
 
   node-releases@2.0.27: {}
 
+  nodemailer@8.0.2: {}
+
   normalize-path@3.0.0: {}
 
   object-assign@4.1.1: {}