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/symbol_registry/competitors.py

@@ -53,6 +53,9 @@ class CompetitorRelationship(BaseModel):
     active: bool
     created_at: datetime
     updated_at: datetime
+    # Enriched from companies table
+    ticker: str | None = None
+    legal_name: str | None = None
 
 
 def _row_dict(row: asyncpg.Record) -> dict[str, Any]:
@@ -128,18 +131,31 @@ async def create_competitor(company_id: str, body: CompetitorRelationshipCreate,
 
 @router.get("/companies/{company_id}/competitors", response_model=List[CompetitorRelationship])
 async def list_competitors(company_id: str, request: Request):
-    """List active competitor relationships for a company, ordered by strength descending."""
+    """List active competitor relationships for a company, ordered by strength descending.
+
+    Enriches each relationship with the ticker and legal_name of the
+    *other* company (the one that isn't company_id).
+    """
     pool = _get_pool(request)
 
     if not await _company_exists(pool, company_id):
         raise HTTPException(404, "Company not found")
 
     rows = await pool.fetch(
-        """SELECT id, company_a_id, company_b_id, relationship_type, strength,
-                  bidirectional, source, active, created_at, updated_at
-           FROM competitor_relationships
-           WHERE (company_a_id = $1 OR company_b_id = $1) AND active = TRUE
-           ORDER BY strength DESC""",
+        """SELECT cr.id, cr.company_a_id, cr.company_b_id,
+                  cr.relationship_type, cr.strength,
+                  cr.bidirectional, cr.source, cr.active,
+                  cr.created_at, cr.updated_at,
+                  c.ticker, c.legal_name
+           FROM competitor_relationships cr
+           LEFT JOIN companies c
+             ON c.id = CASE
+               WHEN cr.company_a_id = $1 THEN cr.company_b_id
+               ELSE cr.company_a_id
+             END
+           WHERE (cr.company_a_id = $1 OR cr.company_b_id = $1)
+             AND cr.active = TRUE
+           ORDER BY cr.strength DESC""",
         company_id,
     )
     return [_row_dict(r) for r in rows]