Add AI stack configuration: ELAI avatars, system params, training tips import

- Add ELAI avatar seed data (7 avatars with codes, URLs, voice configs)
  from the original backend's avatars.json
- Add missing system parameters: encoach.aws_region (eu-west-1),
  encoach.whisper_workers (4)
- Add training tips import script with pathways_2_rw.json data source
- Add action_compute_embeddings() method to training tip model for
  computing sentence-transformer embeddings on demand

Made-with: Cursor

encoach_core/data/constants.xml

@@ -32,6 +32,19 @@
             <field name="key">encoach.gptzero_api_key</field>
             <field name="value"></field>
         </record>
+
+        <!-- AWS region for Polly TTS -->
+        <record id="param_aws_region" model="ir.config_parameter">
+            <field name="key">encoach.aws_region</field>
+            <field name="value">eu-west-1</field>
+        </record>
+
+        <!-- Whisper STT worker count -->
+        <record id="param_whisper_workers" model="ir.config_parameter">
+            <field name="key">encoach.whisper_workers</field>
+            <field name="value">4</field>
+        </record>
+
         <record id="param_stripe_secret" model="ir.config_parameter">
             <field name="key">encoach.stripe_secret_key</field>
             <field name="value"></field>