refactor: hard-cut RSS infrastructure (scope C)

Removes the entire RSS feature surface — feeds, items, embeddings, reactions,
discussion-note flow, briefing news context, settings, env-vars, and DB
tables. Keeps the URL-generic article-reader (the read_article LLM tool)
under a clean module so the LLM can still fetch arbitrary article content
from URLs the user provides.

Backend:
- New services/article_fetcher.py — single source of trafilatura URL→text
- New services/tools/article.py — read_article tool (was nested under tools/rss)
- Delete services/rss.py, rss_classifier.py, rss_filtering.py, article_context.py
- Delete services/tools/rss.py
- Delete models/rss_feed.py (RssFeed, RssItem), models/rss_item_embedding.py
- services/embeddings.py: drop upsert/semantic_search/backfill RSS helpers
- services/llm.py: remove _build_briefing_article_context, briefing-conv branch,
  ARTICLE_DISCUSS_SEED skip-RAG branch; drop get_rss_items / add_rss_feed from
  the actions list
- services/generation_task.py: drop _maybe_save_article_discussion_note + caller
- routes/chat.py: drop /api/chat/from-article/<id> endpoint
- routes/journal.py: re-import via web.py refactor (article_fetcher path)
- services/tools/__init__.py: register `article`, drop `rss`
- services/tools/_registry.py: drop the requires=='rss' check
- app.py: drop backfill_rss_item_embeddings + backfill_rss_article_content tasks
- config.py: prose-only edit (no env var change — RSS env vars were never first-class)

Frontend:
- stores/settings.ts: drop rssEnabled
- SettingsView.vue: drop the RSS-classification mention
- api/client.ts: drop openArticleInChat (the from-article endpoint is gone)

Tests:
- Delete tests/test_rss_service.py, test_news_api.py, test_article_reading.py

Migration:
- 0042_drop_rss: DROP TABLE rss_item_embeddings, rss_item_reactions, rss_items,
  rss_feeds; DELETE settings rows for rss_enabled / briefing_*_topics

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/fabledassistant/routes/chat.py

@@ -507,81 +507,3 @@ async def delete_model_route():
         return jsonify({"error": str(e)}), 500
 
 
-@chat_bp.route("/from-article/<int:item_id>", methods=["POST"])
-@login_required
-async def create_conversation_from_article(item_id: int):
-    """Create a chat conversation seeded for article discussion and auto-run.
-
-    Mirrors the briefing ``discuss_article`` route: creates a fresh
-    conversation, stages the shared synthetic read_article exchange + seed
-    prompt, then kicks off generation so the client lands on an in-flight
-    stream. The Flutter and web chat screens reconnect to the running buffer
-    on mount.
-    """
-    from sqlalchemy import select as _select
-    from fabledassistant.models import async_session as _async_session
-    from fabledassistant.models.rss_feed import RssItem, RssFeed
-    from fabledassistant.services.article_context import (
-        EmptyArticleError,
-        seed_article_discussion,
-    )
-
-    uid = get_current_user_id()
-
-    async with _async_session() as session:
-        result = await session.execute(
-            _select(RssItem)
-            .join(RssFeed, RssItem.feed_id == RssFeed.id)
-            .where(RssItem.id == item_id, RssFeed.user_id == uid)
-        )
-        item = result.scalars().first()
-
-    if item is None:
-        return jsonify({"error": "Article not found"}), 404
-
-    conv_title = (item.title or "Article discussion")[:80]
-    conv = await create_conversation(uid, title=conv_title, conversation_type="chat")
-
-    model = await get_setting(uid, "default_model", "") or Config.OLLAMA_MODEL
-    try:
-        discuss_prompt = await seed_article_discussion(conv.id, item, model)
-    except EmptyArticleError as e:
-        # Roll back the empty conversation so the user doesn't end up with a
-        # phantom entry in their chat list.
-        try:
-            await delete_conversation(uid, conv.id)
-        except Exception:
-            logger.warning("Failed to clean up empty article conversation %s", conv.id)
-        return jsonify({"error": str(e)}), 422
-
-    # Reload conversation so we see the two messages the helper just added.
-    conv = await get_conversation(uid, conv.id)
-    assert conv is not None
-
-    history: list[dict] = []
-    for msg in conv.messages:
-        if msg.role == "system":
-            continue
-        msg_dict: dict = {"role": msg.role, "content": msg.content or ""}
-        if msg.tool_calls:
-            msg_dict["tool_calls"] = [
-                {"function": {"name": tc["function"], "arguments": tc["arguments"]}}
-                for tc in msg.tool_calls
-            ]
-            history.append(msg_dict)
-            for tc in msg.tool_calls:
-                history.append({"role": "tool", "content": json.dumps(tc.get("result", {}))})
-        else:
-            history.append(msg_dict)
-
-    assistant_msg = await add_message(conv.id, "assistant", "", status="generating")
-    buf = create_buffer(conv.id, assistant_msg.id)
-    asyncio.create_task(run_generation(
-        buf, history, model, uid, conv.id, conv.title or "", discuss_prompt,
-    ))
-
-    return jsonify({
-        "conversation_id": conv.id,
-        "assistant_message_id": assistant_msg.id,
-        "status": "generating",
-    }), 202