session symbols: syminfo-tz session windows, symbol-clock D/W/M anchors, zero-lot orders, margin call at the open

[luisleo526]

Four generic session-symbol semantics fixes, measured on the NASDAQ:AAPL and OANDA:EURUSD 15m populations and byte-inert on BINANCE:ETHUSDT.P (24x7/UTC) — ETH scraped 396/396 and corpus 309/2/1 unchanged.

1. time(tf, session) / time_close session windows read in syminfo.timezone (finding 421/436). The session-filter tz defaulted to UTC; Pine resolves it in the exchange tz. Engine side: pine_time/pine_time_close gain a trailing syminfo_tz (default "" = old behaviour; feature macro PF_PINE_TIME_HAS_SYMINFO_TZ). Codegen PR passes syminfo_.timezone.
2. Zero-lot orders are not placed (finding 426/438). An entry or pyramiding add whose lot-floored quantity is 0 was admitted as a phantom qty-0 position (opentrades==1, position_size==0), silently blocking every later signal. TV simply does not place it.
3. Symbol-clock D/W/M anchors for ta.vwap, timeframe.change, time('D'|'W'|'M') (finding 423/440). These keyed on UTC midnight; for OANDA:EURUSD the trading day rolls 17:00 ET and the week opens Sun 17:00 ET. New helpers (session_day_index, session_period_open_ms/close_ms) built on the security: anchor HTF aggregation on the symbol clock (syminfo.timezone + session) #159–security: session-attributed weekly/monthly period keys #161 machinery; VWAP::compute (tz,session) overloads, 7-arg pine_time (macros PF_PINE_TIME_HAS_SESSION_DAY, PF_VWAP_HAS_SESSION_ANCHOR). Semantic decisions pending a TV probe are listed in finding 440 (valid explicit session defines the day in its own tz; wrapped-session month attribution).
4. Forced liquidation at the bar open for carried leveraged positions (finding 430/441). TV fires the margin-call slice at the OPEN when the open already breaches (then a second slice at the extreme); the engine only checked the extreme. Rule fitted on 8,414 AAPL margin-call events (8,403 qty-exact).

Population evidence (lab findings 443–445; ladder-ranking harness 90fcb64): EURUSD excellent 251 → 271, e+s 327 → 347, 30 tier ups / 0 downs; AAPL excellent 210 → 235, e+s 291 → 307, 31 up / 5 down. Four-lane symbol gate PASS vs the 08-22 baseline (aapl 170 up / 19 down, eurusd 79 up / 36 down).

Tests: ctest green incl. new test_zero_lot_entry_decline, test_session_day_anchors (23,850 checks), test_margin_call_gap_open, session_time DST cases.