fix: show a block's events, joined to the extrinsics that caused them

The block page listed extrinsics and nothing else. Block 1 holds twenty-eight
indexed events and the route returned none of them — visible from the outside,
because an account page linked to a `Wormhole::NativeTransferred` at block 1 and
block 1 showed no sign of it.

`phase` and `extrinsic_index` were stored for exactly this join and had never
been used. Each extrinsic now carries its own events beneath it, and the block's
own events sit in their phases.

Block 1 is the argument for doing it that way. As extrinsics alone it is a
single `Timestamp::set`. Its events are the entire opening distribution:
twenty-one `Wormhole::NativeTransferred` in `Initialization`, owned by no
extrinsic at all and sent from the minting account — not block zero, and not
anything a transaction did. `Vesting::LaunchMomentSet` fires there too, so
vesting has been exercised despite the call index showing zero `Vesting::*`
dispatched: a pallet the runtime uses looks unused from the call side alone.

Closes #3

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jp6a8EDar9ueEhAxzep4V5

.sqlx/query-c248c9698587376f96478c61af945d52e8e2678fd1ad7127dcd27915e258c19f.json

@@ -0,0 +1,71 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n            select height, event_index, pallet, variant, phase, extrinsic_index,\n                   fields as \"fields!\", at, accounts as \"accounts!\"\n            from chain_event\n            where chain = $1 and height = $2\n            order by event_index asc\n            ",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "height",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 1,
+        "name": "event_index",
+        "type_info": "Int4"
+      },
+      {
+        "ordinal": 2,
+        "name": "pallet",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 3,
+        "name": "variant",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 4,
+        "name": "phase",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 5,
+        "name": "extrinsic_index",
+        "type_info": "Int4"
+      },
+      {
+        "ordinal": 6,
+        "name": "fields!",
+        "type_info": "Jsonb"
+      },
+      {
+        "ordinal": 7,
+        "name": "at",
+        "type_info": "Timestamptz"
+      },
+      {
+        "ordinal": 8,
+        "name": "accounts!",
+        "type_info": "TextArray"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Text",
+        "Int8"
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      false,
+      false,
+      false,
+      true,
+      false,
+      true,
+      false
+    ]
+  },
+  "hash": "c248c9698587376f96478c61af945d52e8e2678fd1ad7127dcd27915e258c19f"
+}