Hardcoded `dialect: "snowflake"` across altimate-core tools

[suryaiyer95]

Problem

The altimate-core tools don't expose a dialect parameter — they always target Snowflake internally. The sql_quality telemetry event supports an optional dialect field, but only the sql-* tools (analyze, optimize, schema-diff) populate it since they accept dialect as a user parameter.

Tools missing dialect support

• altimate-core-validate.ts
• altimate-core-fix.ts
• altimate-core-correct.ts
• altimate-core-semantics.ts
• altimate-core-equivalence.ts
• altimate-core-policy.ts
• altimate-core-check.ts
• impact-analysis.ts

Tools that already support dialect

• sql-analyze.ts — dialect parameter, passed to dispatcher and telemetry
• sql-optimize.ts — same
• schema-diff.ts — same

Proposed fix

1. Add an optional dialect parameter to all altimate-core tools (defaulting to "snowflake")
2. Pass the dialect through to the Dispatcher call
3. Include dialect in metadata so telemetry picks it up

This enables per-dialect telemetry segmentation and prepares these tools for multi-dialect support (postgres, bigquery, duckdb, etc.).

Context

Identified during PR #446 (sql_quality telemetry). Rather than hardcoding dialect: "snowflake", we made the telemetry field optional — tools that don't set it simply omit it from the event.