feat(p3): CLI watch registration, pool stats API, JSON function parsing (#458 #459 #460)

Part A (#458): Register watch command in CLI root
- Added cmd/gosqlx/cmd/watch_cmd.go with cobra command wrapping existing FileWatcher
- Supports --mode (validate|format), --debounce, --clear, --watch-verbose flags
- gosqlx watch now appears in --help output

Part B (#460): Pool utilization stats API
- Added pkg/metrics/pool_stats.go: PoolStat struct, RecordNamedPoolGet/Put, GetPoolStats, ResetPoolStats
- Instrumented tokenizer, parser, and AST pools with RecordNamedPoolGet/Put calls
- Added cmd/gosqlx/cmd/stats.go: gosqlx stats command with human-readable table and --json flag
- Added pkg/metrics/pool_stats_test.go with 8 race-safe tests including concurrent safety

Part C (#459): JSON function parsing tests
- Added pkg/sql/parser/json_functions_test.go: 12 tests covering JSON_OBJECT, JSON_BUILD_ARRAY,
  JSON_EXTRACT, JSON_AGG, JSON_BUILD_OBJECT, JSON_VALUE, JSON_CONTAINS, JSON_SET, JSONB_AGG,
  TO_JSON, JSON_ARRAYAGG, JSON_LENGTH, and arrow operators (all PASS)
- Parser already handles JSON functions as generic FunctionCall nodes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 2 people

CHANGELOG.md

@@ -8,6 +8,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- **Live schema introspection** (`pkg/schema/db`): New `Loader` interface and `DatabaseSchema`/`Table`/`Column`/`Index`/`ForeignKey` types for querying live database metadata
+- **PostgreSQL schema loader** (`pkg/schema/postgres`): Introspects tables, columns (with primary/unique flags), indexes, and foreign keys via `information_schema` and `pg_catalog`
+- **MySQL schema loader** (`pkg/schema/mysql`): Introspects tables, columns, indexes, and foreign keys via `information_schema`
+- **SQLite schema loader** (`pkg/schema/sqlite`): Introspects tables, columns, indexes, and foreign keys via PRAGMA commands (pure Go, no cgo required)
+- **`gosqlx.LoadSchema()`** top-level convenience wrapper for dialect-agnostic schema loading
+- Integration tests using `testcontainers-go` v0.32.0 for PostgreSQL and MySQL loaders
 - **MariaDB dialect** (`--dialect mariadb`): New SQL dialect extending MySQL with support for SEQUENCE DDL (`CREATE/DROP/ALTER SEQUENCE` with full option set), temporal tables (`FOR SYSTEM_TIME`, `WITH SYSTEM VERSIONING`, `PERIOD FOR`), and `CONNECT BY` hierarchical queries with `PRIOR`, `START WITH`, and `NOCYCLE`
 
 ## [1.13.0] - 2026-03-20