Rewrite Python comments in Google developer documentation style (#12)

* Rewrite comments in Google developer documentation style

Rewrite the comments and docstrings across the backend core modules so they
read plainly. The previous prose was accurate but dense and figurative, which
made it slow to skim.

Applies the Google developer documentation style guide: short sentences, active
voice, present tense, American spelling, and no metaphors, idioms, or
rhetorical asides. Replaces em-dash chains with separate sentences.

backend/app/scripting/pipeline.py

@@ -24,19 +24,20 @@ class ScriptPipeline:
         return msg if isinstance(msg, str) and msg.strip() else None
 
     def _history(self) -> list[dict]:
-        # The path, not `adventure.actions` — that collection is every branch's
-        # actions, and this is the documented history API a user script reads.
-        # Handing a script the siblings of the turn it is running on would be
-        # the same bug as building a prompt from them, only user-visible.
+        # Read the path rather than `adventure.actions`. That collection holds
+        # every branch's actions, and this is the documented history API a user
+        # script reads. Giving a script the siblings of the turn it is running on
+        # would be the same bug as building a prompt from them, and visible to
+        # the user.
         #
-        # `story_actions` also drops blank-text rows, which `adventure.actions`
-        # kept, so this array is shorter than it used to be for an adventure
-        # that has any — and `info.actionCount` counts the same way. That is
-        # deliberate: a row with no text is this app's bookkeeping, it has no
-        # counterpart in the AI Dungeon history a ported script was written
-        # against, and the prompt has never included one. A script keyed on
-        # "every N actions" will land on different turns than it did before
-        # phase 14; there is no reading of this that is compatible with both.
+        # `story_actions` also drops rows with blank text, which
+        # `adventure.actions` kept, so this array is shorter than it was for an
+        # adventure that has any such rows. `info.actionCount` counts the same
+        # way. That is intended. A row with no text is this app's bookkeeping, it
+        # has no counterpart in the AI Dungeon history a ported script was
+        # written against, and the prompt has never included one. A script keyed
+        # on every N actions lands on different turns than it did before phase
+        # 14, and no reading of this is compatible with both.
         return [
             {"text": a.text, "rawText": a.text, "type": a.type}
             for a in context_history.story_actions(self.adventure)