feat: add file attachment support to issue tracker with Gitea mirroring

Implement full attachment CRUD for issues and comments, restricted to open issues only. Attachments are stored locally and mirrored to the Gitea tracker via new `mirror_attachment_to_gitea` and `set_gitea_asset_id` functions. Add `gitea_asset_id` column to the attachments table, extend `IssueForm` and `IssueCommentForm` with `attachment_uids` field, and expose new API endpoints for listing, adding, and deleting issue attachments. Update agent configuration to include web research tools, and document the new capability in README, AGENTS.md, and CLAUDE.md.

tests/e2e/issues/attachments.py

@@ -0,0 +1,36 @@
+# retoor <retoor@molodetz.nl>
+
+import io
+import re
+
+from PIL import Image
+from playwright.sync_api import expect
+
+from tests.conftest import BASE_URL
+
+
+def _png():
+    buf = io.BytesIO()
+    Image.new("RGB", (8, 8), (0, 128, 255)).save(buf, "PNG")
+    return buf.getvalue()
+
+
+def test_create_modal_collects_attachment_uid(alice):
+    page, _ = alice
+    page.goto(f"{BASE_URL}/issues", wait_until="domcontentloaded")
+    page.click("button[data-modal='create-issue-modal']")
+    page.locator("#create-issue-modal").wait_for(state="visible")
+    file_input = page.locator(
+        "#create-issue-modal dp-upload .dp-upload-input"
+    ).first
+    file_input.set_input_files(
+        {"name": "shot.png", "mimeType": "image/png", "buffer": _png()}
+    )
+    page.locator(
+        "#create-issue-modal dp-upload .dp-upload-count"
+    ).first.wait_for(state="visible", timeout=15000)
+    expect(
+        page.locator(
+            "#create-issue-modal dp-upload input[name='attachment_uids']"
+        )
+    ).to_have_value(re.compile(r".+"))