fix(actions): keep small foreign dividends, allow only read paths, show open offers

From Pullfrog's review of #78:

- A dividend in another currency keeps 6 decimals (USD 0.0012 was rounded
  to 0.0 in JSON and "USD 0" in the table); rupiah stays to the sen.
- `--kind stock_dividend` and `--kind reverse_split` work on the CLI too,
  as they already did over MCP.
- The session client GETs only the prefixes in READ_PATHS, as
  docs/STOCKBIT.md's rule 1 already said: any other path (orders, PIN,
  withdrawals) fails before a request or token refresh leaves the process.
- `stocks calendar` and get_corporate_calendar also list rights trading,
  tender offers and IPO offers still open in the range, so an offer that
  began earlier shows while it can be acted on. A warrant's years-long
  windows do not count. The 2026-11-03..12 golden gains DOOH, NAYZ and AUTO.
- `stocks calendar --help` names the ex-date fallback, and docs/STOCKBIT.md
  shows the record and surface as shipped.

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

docs/ARCHITECTURE.md

@@ -296,8 +296,10 @@ WIB as the fallback.
   request per kind, cached 6 hours under `stockbit-corpaction`
   (`<kind>:<SYMBOL.JK>` or `<kind>:market`); `stocks actions` /
   `get_corporate_actions` sort newest first, `stocks calendar` /
-  `get_corporate_calendar` filter by `CorporateAction::date` (the cum date
-  for entitlements) and sort oldest first. Endpoint notes and the wider
+  `get_corporate_calendar` keep what `CalendarRange::includes`: a
+  `CorporateAction::date` (the cum date for entitlements) in the range, or a
+  rights, tender or IPO `period` that overlaps it (not a warrant's, which
+  runs for years), sorted oldest first. Endpoint notes and the wider
   design: `docs/STOCKBIT.md`.
 
 ### Capability Gating