feat(imap): add attachment type filter for IMAP ingestion

Add a configurable switch to control which attachment types are ingested
via IMAP. Images are excluded by default; office files and PDFs are ingested.

- Add global `IMAP_ATTACHMENT_FILTER` config setting (default: `documents_only`)
- Add `attachment_filter` column to `UserImapAccount` model for per-user override
- Migration 032 adds the column to `user_imap_accounts` table
- Update `fetch_attachments_and_enqueue()` to respect filter (documents_only/all)
- Update `pull_inbox()`, `_pull_user_imap_accounts()`, and
  `_pull_user_integration_imap()` to pass the resolved filter
- Update IMAP accounts API (schemas, create/update handlers, response serializer)
- Update IMAP accounts UI to show attachment filter dropdown in modal and
  display filter badges on account cards
- Add 6 new tests covering attachment filter behaviour
- Update ConfigurationGuide.md, EmailIngestion.md, and .env.demo

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/api/imap_accounts.py

@@ -110,6 +110,15 @@ class ImapAccountCreate(BaseModel):
     use_ssl: bool = Field(default=True, description="Use SSL/TLS connection")
     delete_after_process: bool = Field(default=False, description="Delete emails from mailbox after processing")
     is_active: bool = Field(default=True, description="Whether to poll this mailbox")
+    attachment_filter: str | None = Field(
+        default=None,
+        description=(
+            "Controls which attachment types to ingest. "
+            "'documents_only' – PDFs and office files only (default when None). "
+            "'all' – all supported types including images. "
+            "Null inherits the global imap_attachment_filter setting."
+        ),
+    )
 
 
 class ImapAccountUpdate(BaseModel):
@@ -123,6 +132,15 @@ class ImapAccountUpdate(BaseModel):
     use_ssl: bool | None = None
     delete_after_process: bool | None = None
     is_active: bool | None = None
+    attachment_filter: str | None = Field(
+        default=None,
+        description=(
+            "Controls which attachment types to ingest. "
+            "'documents_only' – PDFs and office files only. "
+            "'all' – all supported types including images. "
+            "Null or empty string clears the override (inherits global setting)."
+        ),
+    )
 
 
 class ImapTestRequest(BaseModel):
@@ -155,6 +173,7 @@ def _to_response(acct: UserImapAccount) -> dict[str, Any]:
         "use_ssl": acct.use_ssl,
         "delete_after_process": acct.delete_after_process,
         "is_active": acct.is_active,
+        "attachment_filter": acct.attachment_filter,
         "last_checked_at": acct.last_checked_at.isoformat() if acct.last_checked_at else None,
         "last_error": acct.last_error,
         "created_at": acct.created_at.isoformat() if acct.created_at else None,
@@ -222,6 +241,7 @@ def create_imap_account(
         use_ssl=body.use_ssl,
         delete_after_process=body.delete_after_process,
         is_active=body.is_active,
+        attachment_filter=body.attachment_filter or None,
     )
     try:
         db.add(acct)
@@ -277,6 +297,12 @@ def update_imap_account(
         acct.delete_after_process = body.delete_after_process
     if body.is_active is not None:
         acct.is_active = body.is_active
+    # attachment_filter uses a sentinel check: the field is always present in the
+    # model (defaulting to None in Pydantic) so we update it unconditionally when
+    # the caller sends any value (including explicit null to clear the override).
+    # An empty string is normalised to None to avoid storing a non-meaningful value.
+    if "attachment_filter" in body.model_fields_set:
+        acct.attachment_filter = body.attachment_filter or None
 
     # Reset last_error so the next poll gives a fresh result
     acct.last_error = None