docs: update CHANGELOG.md covering revival changes (issues #2-#28)

[dtsong]

Problem

13 issues closed and 16 PRs merged since the community revival (March 2026) with zero CHANGELOG updates. Users and contributors cannot assess project health or what has changed.

Scope

Update CHANGELOG.md with entries for:

• Security fixes (Security: Remove hardcoded TrustServerCertificate in MSSQL driver #2 MsSQL hardcoded certs, fix: make Compiler thread-safe and fix CI infrastructure #18 thread safety)
• Bug fixes (Thread-safety: _subqueries dict in Compiler is not thread-safe #3 thread safety, Missing type validation in joins and set operations #5 type validation, Fragile datetime parsing via string slicing #6 datetime parsing, Incomplete collation comparison logic #8 collation, CTE schema not properly registered #9 CTE schema, PostgreSQL: Handle timestamp edge cases #12 PG timestamps, Presto: Incomplete rounding implementation #13 Presto rounding, fix: Cte.schema return type and use safezip #22 CTE schema, fix: harden schema property error handling across AST classes #23 schema properties)
• Cleanup (Remove deprecated compile() wrapper method #7 deprecated compile, Dead code: Param class may be unused #10 dead code)
• Infrastructure (feat: Docker Compose local test infrastructure with seed data #24 Docker Compose, fix: harden schema properties and add CODE_MAP.md #25 CODE_MAP, docs: add CLAUDE.md and Windows compatibility note #27 CLAUDE.md)
• Core revival (Community Revival: Modernize data-diff as v1.0.0 #1 v1.0.0, chore: clean up stale Datafold references and docs #14 Datafold cleanup)

Acceptance Criteria

• CHANGELOG covers all merged PRs since revival
• Entries follow Keep a Changelog format
• Security fixes are prominently noted