fix: blank company charts + competitor GUIDs instead of tickers

Trend charts blank:
- trend_windows uses upsert (1 row per ticker/window), so charts had
  at most 1 data point. Added trend_history table (migration 024) that
  appends every snapshot. New /api/trends/history endpoint serves the
  time series. Frontend now uses useTrendHistory for charts and
  useTrends for the latest summary card.

Competitor GUIDs:
- list_competitors query returned raw company_b_id UUIDs without
  joining companies table. Added LEFT JOIN with CASE to resolve the
  other company's ticker and legal_name. Updated Pydantic model to
  include enriched fields. Frontend fallback changed from truncated
  UUID to ticker/legal_name/Unknown.

services/api/app.py

@@ -415,6 +415,56 @@ async def list_trends(
     return results
 
 
+@app.get("/api/trends/history")
+async def list_trend_history(
+    ticker: Optional[str] = None,
+    window: Optional[str] = None,
+    limit: int = Query(default=200, le=1000),
+):
+    """Return historical trend snapshots for charting.
+
+    Unlike /api/trends which returns the latest snapshot per entity/window,
+    this endpoint returns the time series from the trend_history table.
+    """
+    conditions: list[str] = []
+    params: list[Any] = []
+    idx = 1
+
+    if ticker:
+        conditions.append(f"entity_id = ${idx}")
+        params.append(ticker.upper())
+        idx += 1
+    if window:
+        conditions.append(f"\"window\" = ${idx}")
+        params.append(window)
+        idx += 1
+
+    where = ("WHERE " + " AND ".join(conditions)) if conditions else ""
+
+    try:
+        rows = await pool.fetch(
+            f"""SELECT id, entity_type, entity_id, "window", trend_direction,
+                       trend_strength, confidence, contradiction_score,
+                       dominant_catalysts, material_risks, generated_at
+                FROM trend_history
+                {where}
+                ORDER BY generated_at ASC
+                LIMIT ${idx}""",
+            *params, limit,
+        )
+    except Exception:
+        # Table may not exist yet (pre-migration 024)
+        return []
+
+    results = []
+    for r in rows:
+        d = _row_to_dict(r)
+        d["dominant_catalysts"] = _parse_jsonb(d.get("dominant_catalysts"))
+        d["material_risks"] = _parse_jsonb(d.get("material_risks"))
+        results.append(d)
+    return results
+
+
 @app.get("/api/trends/{trend_id}")
 async def get_trend(trend_id: str):
     """Get a single trend summary by ID."""