fix(actions): JSON kinds match --kind, and harden parsing and ranges

- JSON named kinds by their Rust names (public_expose, tender_offer,
  stock_dividend, reverse_split) while --kind and MCP take expose, tender,
  stock-dividend, reverse-split, so an output kind could not be passed
  back. JSON now uses the input names; old cache entries still read, and
  --kind also accepts underscores.
- {"dividend": null, "today": "..."} failed to parse and aborted the
  whole command; a null list beside scalars now reads as none.
- An extreme --from panicked on the default 30 days; it is an error now.
  The 366-day limit let 367 days through; it counts both ends now.
- An entitlement without a cum date sat on its ex date under a note that
  calls DATE the cum date. The table marks it (ex) and says what that
  means; JSON leaves cum_date out, as before, and the docs say so.
- A dividend's currency was ignored; one not in IDR now carries currency
  and the table shows it instead of Rp.
- The live check no longer fails a quiet month's empty calendar.

Claude-Session: https://claude.ai/code/session_01RqPPVeVDrnLoP7NUZmLRxY

crates/idx-mcp/src/server.rs

@@ -358,8 +358,9 @@ average price, the close, `change_bps` and `non_regular_bps`."
         description = "Corporate actions of one IDX stock from the user's own Stockbit \
 session, newest first: `kind` (dividend, stock-dividend, bonus, rights, warrant, split, \
 reverse-split, meeting, expose, ipo, tender), `date` (the cum date for dividends, bonuses, \
-rights and splits, i.e. the last day to buy and be entitled; else the event's first day), \
-`ex_date`, `record_date`, `pay_date`, and per kind `cash_per_share` (IDR, may have decimals), \
+rights and splits, i.e. the last day to buy and be entitled, or the ex date when `cum_date` \
+is absent; else the event's first day), `ex_date`, `record_date`, `pay_date`, and per kind \
+`cash_per_share` (IDR, may have decimals; in `currency`, an ISO code, when that is present), \
 `ratio` {old, new} (1:5 split = 1 share becomes 5; 655:104 rights = 104 rights per 655 held), \
 `factor` (price adjustment), `price` (rights, warrant exercise, tender or IPO price, IDR), \
 `period` and `exercise` {start, end}, `shares`, `percentage_bps`, `time`, `venue`. Absent \