Enforce British English spelling in all agent prompt templates

Added explicit UK English instruction to the Response Format section of
all five agents (legal, brand, channel best practices, channel tech specs,
lead) so output uses spellings like "authorised", "colour", "capitalise".

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

backend/app/agents/brand_agent.py

@@ -146,6 +146,7 @@ If the proof is nonsensical, not a marketing material, or cannot be analyzed, se
 - Each bullet should be one actionable sentence
 - Start with the issue, then the recommendation
 - Example: "Logo placement incorrect (bottom-left) - move to top-right corner per guidelines"
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 """
 
         # Determine if revision fields should be included

backend/app/agents/channel_best_practices_agent.py

@@ -139,6 +139,7 @@ If the proof is nonsensical, not a marketing material, or cannot be analyzed, se
 - Each bullet should be one actionable sentence
 - Start with the issue, then the recommendation
 - Example: "CTA placement below fold - move above fold for better visibility"
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 """
 
         # Determine if revision fields should be included

backend/app/agents/channel_tech_specs_agent.py

@@ -147,6 +147,7 @@ If the proof is nonsensical, not a marketing material, or cannot be analyzed, se
 - Each bullet should be one actionable sentence
 - Start with the issue, then the specification requirement
 - Example: "Image resolution 72dpi - increase to minimum 150dpi for print quality"
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 """
 
         # Determine if revision fields should be included

backend/app/agents/lead_agent.py

@@ -147,6 +147,7 @@ Your summary should:
 - Each bullet: one sentence, actionable
 - Do NOT include page numbers, document names, or source citations. Keep all feedback self-contained and actionable.
 - For 'Passed': briefly note any amber items in 1-2 bullets
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 {revision_context}
 Here are the specialist reviews:
 {self._format_reviews(reviews)}

backend/app/agents/legal_agent.py

@@ -149,6 +149,7 @@ If the proof is nonsensical, not a marketing material, or cannot be analyzed, se
 - Do NOT include page numbers, document names, or source citations (e.g., no "Page 10", "per the Legal Guidelines"). Feedback must be self-contained and actionable.
 - Start with the issue, then the requirement
 - Example: "Missing APR disclaimer - add representative APR per FCA requirements"
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 """
 
         # Determine if revision fields should be included