fix(mcp): unresolved symbols, finite options validation, row cap (HKUDS#120)

* fix(mcp): surface unresolved market-data symbols

A typo / wrong-suffix / delisted / no-data code vanished from
get_market_data's result (the dict only held winners), so it was
indistinguishable from "no data", and a loader exception lost every
already-resolved symbol (P05).

Report any requested code that produced nothing under a reserved
`_unresolved` key (additive — omitted when all codes resolve, so the
all-resolved payload is byte-identical to before) and wrap the
per-group loader.fetch so a blow-up is contained, not opaque. Richer
per-symbol status objects are a deliberate breaking follow-up.

(cherry picked from commit eba2044e982c5d467c808bad05386de3d856d635)

* fix(tools): reject invalid analyze_options inputs

Invalid inputs (volatility<=0, spot/strike<=0, negative expiry,
bad option_type) and T=0 all returned status:"ok" with silently
wrong / zeroed Greeks, and NaN could leak into the JSON (P06).

Validate at the boundary and reject invalid inputs with an error
envelope; flag the legitimate T=0 expiry as status:"degenerate"
with a warning (intrinsic value still returned); serialize with
allow_nan=False. The normal path is numerically unchanged. The
Greeks-convention rework (delta=0.5 at expiry) is a larger
follow-up, out of scope here.

(cherry picked from commit 823dc2382d73b97919807cf14a3644073886247d)

* fix(mcp): cap get_market_data row output

Every row of every symbol was emitted, so the canonical "1 symbol,
1 year, daily" request (~251 rows) breached the MCP token budget and
had to spool to a file, defeating an inline data tool (P07).

Add a max_rows cap (default 250): a symbol exceeding it returns a
head+tail window plus truncation metadata (rows/returned/truncated/
hint); symbols within the cap are unchanged (plain list, so small
queries are byte-identical); max_rows=0 restores the unbounded legacy
behavior. Columnar encoding and envelope de-duplication are broader
follow-ups, out of scope here.

(cherry picked from commit 0e426b1d0523e8c8144c699f89cd4847199e6448)

* fix(options): reject nan/inf + log dropped loader

options_pricing previously accepted NaN/Inf numeric inputs and
silently produced unreliable Greeks. Reject any non-finite spot,
strike, expiry_days, volatility, or risk_free_rate at the
validation boundary before pricing, and treat a missing result
key as non-finite so a dropped field is flagged degenerate
instead of defaulting to a confident 0.0.

mcp_server.get_market_data: the contained loader-failure path
(P05) now logs the swallowed exception with logger.exception
instead of vanishing silently; the _unresolved fallthrough is
unchanged.

* fix(mcp): stride row cap, reject neg max_rows

_cap_rows previously returned a head+tail window with a synthetic
{_gap: N} sentinel, hiding the middle of the series and emitting a
fake non-bar record. Replace with an even-stride downsample (every
step-th bar, last bar pinned) so the capped series spans the full
date range with only real bars.

A negative max_rows now enforces the default cap instead of being
treated as <=0 (which silently disabled the cap and returned an
unbounded payload). max_rows=0 still means unbounded; the in-cap
plain-list path is unchanged.

Author: Teerapat-Vatpitak