refactor: rename gitclaw adapter/format to gitagent

[Nivesh353]

Summary

Renames the gitclaw export adapter/format to gitagent across code and docs.

Changes

• Renamed src/adapters/gitclaw.ts and src/runners/gitclaw.ts → gitagent.ts (symbols, comments, spawned CLI, install hint updated)
• Updated format/adapter keyword gitclaw → gitagent in commands/export.ts, commands/run.ts, and adapters/index.ts
• Updated docs: README.md, docs.md, and paper/*

How I tested

Built locally and ran the CLI via node dist/index.js from the repo root:

• npm run build — compiles clean
• grep -rin gitclaw (excl. dist/node_modules) — no leftover references
• node dist/index.js export -f gitagent -d examples/standard — produces correct output; -f gitclaw now errors as expected
• node dist/index.js run -a gitagent -d examples/standard -p "hi" — prepares workspace and launches the agent
• node dist/index.js export --help / run --help — show gitagent, no gitclaw