feat: add pipeline engine with approval flow and file triggers

Sequential step executor (script, claude_prompt, approval, api_call,
template, skyvern placeholder), reaction-based approvals, file upload
trigger matching, portal API state sync.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pipelines/approval.py

@@ -0,0 +1,18 @@
+"""Approval handling — maps Matrix reactions to pipeline approvals."""
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+# Reaction emoji to response mapping
+APPROVAL_REACTIONS = {
+    "\U0001f44d": "approve",       # thumbs up
+    "\U0001f44e": "decline",       # thumbs down
+    "\u2705": "approve",           # check mark
+    "\u274c": "decline",           # cross mark
+}
+
+
+def reaction_to_response(reaction_key: str) -> str | None:
+    """Map a reaction emoji to an approval response."""
+    return APPROVAL_REACTIONS.get(reaction_key)