Schema 1.5.0: holiday calendar registry, citext names; drop num_records

For the coverage-aware holiday-calendar API in TSAPI core (db_base
holiday_calendar__get / __set_coverage / __set_metadata / __upsert).

- meta.holiday_calendars (name, description, covered_from, covered_to,
  source, updated_at): a calendar exists when it has a row here, not
  when it has holidays (retires the 9999-12-31 sentinel row).
  covered_from/to: the range over which the closure list is complete;
  both set or both NULL, from <= to (holiday_calendars_coverage_check).
- Calendar names are citext in every table (registry, holidays.calendar_name,
  exchanges.default_holiday_calendar, instruments.holiday_calendar):
  stored as given, unique and matched case-insensitively -- also in the
  foreign keys -- as the native TSAPI backend does with COLLATE NOCASE.
  New extension citext (00_extensions.sql). Name check: non-empty,
  trimmed, <= 50 characters.
- FKs: holidays -> registry ON DELETE CASCADE; exchanges/instruments ->
  registry ON DELETE RESTRICT (a calendar in use cannot be dropped);
  ON UPDATE CASCADE everywhere.
- meta.series.num_records dropped. Only some write paths maintained it
  (never C++), it sometimes held an estimate, and it was NULL for a series
  never written to. Clients ask the table: count(*), or
  SELECT EXISTS (SELECT 1 FROM <table>) for "is it empty?".
- find_schema_problems() covers the new table, columns, constraints and
  extension, and runs with search_path = pg_catalog so format_type()
  reports 'public.citext' whatever the caller's search_path.

Verified on a fresh database (PG 17): run_setup.py installs it and
find_schema_problems() returns zero rows, also for a caller without
public on the search_path; constraint behaviour checked by hand
(case-insensitive duplicate refused, FK matches any spelling, RESTRICT
and CASCADE, coverage and name checks).

Re-provision databases (no migration).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sql/03_tables.sql

@@ -38,15 +38,29 @@ CREATE TABLE meta.exchanges (
     currency character varying(3),
     default_sec_type character varying(18),
     default_session character varying(40),
-    default_holiday_calendar character varying(40),
+    default_holiday_calendar public.citext,
     default_tick_size double precision,
     default_tick_value double precision,
     default_extended_hours boolean DEFAULT false,
     country character varying(3)
 );
 
+-- Holiday calendar registry (1.5.0). A calendar exists when it has a row
+-- here -- not when it has holidays. covered_from/covered_to: the range over
+-- which its list of closures is complete (both set, or both NULL = unknown).
+-- Names are citext: stored as given, matched case-insensitively ('NYSE' and
+-- 'nyse' are one calendar), the same rule as the native TSAPI backend.
+CREATE TABLE meta.holiday_calendars (
+    name public.citext NOT NULL,
+    description text,
+    covered_from date,
+    covered_to date,
+    source text,
+    updated_at timestamp with time zone NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
 CREATE TABLE meta.holidays (
-    calendar_name character varying(50) NOT NULL,
+    calendar_name public.citext NOT NULL,
     date date NOT NULL,
     description character varying(255),
     early_close boolean NOT NULL DEFAULT false,
@@ -64,7 +78,7 @@ CREATE TABLE meta.instruments (
     strike double precision,
     currency character varying(3),
     session character varying(40),
-    holiday_calendar character varying(50),
+    holiday_calendar public.citext,
     sec_id character varying(50),
     sec_id_type character varying(20),
     description character varying(255),
@@ -92,6 +106,10 @@ CREATE TABLE meta.schema_version (
     description text
 );
 
+-- No record count is stored (removed in 1.5.0): "num_records" was maintained by
+-- some write paths only, sometimes held an estimate, and was NULL for a series
+-- never written to. Ask the table itself: SELECT count(*), or for "is it empty?"
+-- SELECT EXISTS (SELECT 1 FROM <table>) -- fast, stops at the first row.
 CREATE TABLE meta.series (
     table_id integer DEFAULT nextval('meta._table_meta__table_id_seq'::regclass) NOT NULL,
     db_schema character varying(70) NOT NULL,
@@ -108,7 +126,6 @@ CREATE TABLE meta.series (
     sec_id character varying(30),
     sec_id_type character varying(30),
     create_timestamp timestamp without time zone DEFAULT CURRENT_TIMESTAMP,
-    num_records bigint,
     first_timestamp timestamp without time zone,
     last_timestamp timestamp without time zone,
     bar_type character varying(30),