feat(mcp): page get_ownership_changes and summarize all changes

Between the two latest releases there are 1,568 holder changes. With only
`limit` (up to 2000, ~200 KB), agents that wanted them all overflowed
their tool output: Hermes then paged ticker by ticker (32 calls), and
opencode 1 and 2 did the same and timed out.

- `offset` pages through the rows; responses carry `offset` and
  `next_offset` (null after the last page). Pages cap at 300 rows
  (~40 KB); the over-limit error points to `offset` and `summary`.
- Rows come largest |delta| first, so the first page holds the moves
  that matter rather than tickers starting with A.
- `summary` covers every row: counts by change type, the number of
  tickers, and the ten tickers with the most changes.

The CLI's `ownership changes` is unchanged. tools.json and the website's
MCP pages are regenerated for the new description and parameter.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V3syn2fN2LNo5pvTSqc6eh

crates/idx-mcp/tests/golden/tools.json

@@ -115,7 +115,7 @@
     "name": "get_investor_holdings"
   },
   {
-    "description": "Holder changes (new, exit, increase, decrease) between two KSEI release dates, optionally for one ticker.",
+    "description": "Holder changes (new, exited, increased, decreased) between two KSEI release dates, optionally for one ticker. Rows come largest change first, one page at a time: `summary` covers all of them (counts by type, tickers with the most changes), and `next_offset` is the `offset` for the next page, or null after the last.",
     "inputSchema": {
       "$schema": "https://json-schema.org/draft/2020-12/schema",
       "properties": {
@@ -125,7 +125,17 @@
         },
         "limit": {
           "default": null,
-          "description": "Maximum rows returned (default 200, at most 2000); `total` reports the full count.",
+          "description": "Rows per page (default 200, at most 300); `total` reports the full count.",
+          "format": "uint",
+          "minimum": 0,
+          "type": [
+            "integer",
+            "null"
+          ]
+        },
+        "offset": {
+          "default": null,
+          "description": "Rows to skip, for the next page: the previous response's `next_offset`.",
           "format": "uint",
           "minimum": 0,
           "type": [