docs: Update documentation for CP2 merge request support

Updates project documentation to reflect the complete CP2 feature set
with merge request ingestion and robot mode capabilities.

README.md:
- Add MR-related CLI examples (gi list mrs, gi show mr, gi ingest)
- Document robot mode (--robot flag, GI_ROBOT env, auto-detect)
- Update feature list with MR support and DiffNote positions
- Add configuration section with all config file options
- Expand CLI reference with new commands and flags

AGENTS.md:
- Add MR ingestion patterns for AI agent consumption
- Document robot mode JSON schemas for parsing
- Include error handling patterns with exit codes
- Add discussion/note querying examples for code review context

Cargo.toml:
- Bump version to 0.2.0 reflecting major feature addition

The documentation emphasizes the robot mode design which enables
AI agents like Claude Code to reliably parse gi output for automated
GitLab workflow integration.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Cargo.toml

@@ -20,7 +20,7 @@ serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 
 # CLI
-clap = { version = "4", features = ["derive"] }
+clap = { version = "4", features = ["derive", "env"] }
 dialoguer = "0.12"
 console = "0.16"
 indicatif = "0.18"