docs: Update CHANGELOG for v1.0.0 release

[lykinsbd]

Overview

Update CHANGELOG.md to prepare for v1.0.0 release.

Changes Required

1. Change Header

Current:

## [Unreleased]

New:

## [1.0.0] - 2026-03-01

**🎉 First stable release!**

This release includes breaking changes. See [Migration Guide](docs/migration-v0.2-to-v1.0.md) for upgrade instructions.

2. Add Stability Commitment Section

Add after the breaking changes section:

### 📋 Stability Commitment

cisshgo v1.0.0 and above follows [Semantic Versioning](https://semver.org/):
- No breaking changes in minor/patch releases (1.x.y)
- Deprecated features supported for at least one major version
- Clear migration guides for major version upgrades

3. Enhance Breaking Changes Section

Add migration guidance:

### ⚠️ Breaking Changes

**CLI Flag Renames** - Kong migration changed flag names to kebab-case:
- `-startingPort` → `--starting-port` (short: `-p`)
- `-transcriptMap` → `--transcript-map` (short: `-t`)

**Transcript Map Schema** - Changed from list-of-maps to direct map:
- Old: `platforms: [{name: {...}}]`
- New: `platforms: {name: {...}}`

**Migration:** See [Migration Guide](docs/migration-v0.2-to-v1.0.md) and use `scripts/migrate_transcript_map.py`.

4. Add New Features Summary

Highlight major features added since v0.2.0:

• Inventory system for multi-device topologies
• Scenario-based stateful command responses
• 5 new platform transcripts (ASA, NX-OS, EOS, JunOS, IOS)
• Environment variable support for all CLI flags
• Comprehensive documentation site
• 90% test coverage

Deliverables

• Update changelog header with v1.0.0 and date
• Add stability commitment section
• Enhance breaking changes with migration guidance
• Add new features summary
• Verify all commit references are correct
• Update comparison link at bottom

Related

• Depends on docs: Add migration guide for v0.2.0 to v1.0.0 #84 (migration guide must exist)
• Part of v1.0.0 release preparation