Add BLIGHT:: document-scope triggers and case-insensitive matching

- Split TRIGGER_PATTERN into INLINE_PATTERN (BLIGHT:) and DOCUMENT_PATTERN
  (BLIGHT::), both case-insensitive
- Inline triggers replace only the trigger line (existing behaviour)
- Document-scope triggers replace the entire file; multiple BLIGHT:: triggers
  in one file are processed sequentially, each seeing the previous result
- Updated FAILED_TEMPLATE to two-line format with BLIGHT_FAILED and BLIGHT_ERROR
- Added complete_document() to AIProvider ABC and GeminiProvider with a
  dedicated system prompt instructing the model to return the full document

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

ai/base.py

@@ -4,13 +4,14 @@ from abc import ABC, abstractmethod
 class AIProvider(ABC):
     """Base class for all AI provider implementations.
 
-    To add a new provider, subclass this and implement `complete`, then
-    instantiate your provider in `processor.py` instead of GeminiProvider.
+    To add a new provider, subclass this and implement `complete` and
+    `complete_document`, then instantiate your provider in `processor.py`
+    instead of GeminiProvider.
     """
 
     @abstractmethod
     def complete(self, document: str, instruction: str) -> str:
-        """Process an instruction in the context of a full document.
+        """Process an inline instruction in the context of a full document.
 
         Args:
             document: The full markdown document text (for context).
@@ -19,3 +20,15 @@ class AIProvider(ABC):
         Returns:
             The text to insert in place of the trigger line.
         """
+
+    @abstractmethod
+    def complete_document(self, document: str, instruction: str) -> str:
+        """Apply a document-scope instruction and return the full rewritten document.
+
+        Args:
+            document: The full markdown document text.
+            instruction: The BLIGHT:: instruction extracted from the trigger line.
+
+        Returns:
+            The full rewritten document as a string.
+        """