feat(env): support auto-dumping conversation via FORGE_AUTO_DUMP env var

[tusharmath]

Summary

Add auto-dump support that automatically exports conversation history to JSON or HTML when a task completes, controlled via the FORGE_AUTO_DUMP environment variable.

Context

Previously, users had to manually trigger conversation dumps after each session. This made it cumbersome to consistently capture outputs for logging, auditing, or post-processing. With auto-dump, the export happens automatically at task completion without any extra steps.

Changes

• Added AutoDumpFormat enum (Json, Html) to the domain layer with FromStr parsing
• Added auto_dump: Option<AutoDumpFormat> field to the Environment struct
• Wired FORGE_AUTO_DUMP env var parsing in the infrastructure layer via the existing parse_env mechanism
• Triggered the dump automatically in the UI task-completion handler when auto_dump is set

Key Implementation Details

AutoDumpFormat uses a lenient FromStr implementation — "json", "true", "1", and "yes" all map to JSON format, while "html" maps to HTML. Any unrecognised value is treated as disabled (None). The dump reuses the existing on_dump method, so no new dump logic was needed.

Use Cases

• CI/CD pipelines: Set FORGE_AUTO_DUMP=json to automatically capture structured conversation output after every run
• Audit trails: Set FORGE_AUTO_DUMP=html to generate human-readable HTML reports of completed sessions
• Quick enable: Set FORGE_AUTO_DUMP=true or FORGE_AUTO_DUMP=1 as a boolean-style toggle for JSON output

Testing

# JSON dump on task completion
FORGE_AUTO_DUMP=json forge run "your task"

# HTML dump on task completion
FORGE_AUTO_DUMP=html forge run "your task"

# Boolean-style enable (produces JSON)
FORGE_AUTO_DUMP=true forge run "your task"

# Run unit tests
cargo insta test --accept -p forge_domain -p forge_infra