#3207: fix: use .moltbot for device identity directory

Fixes #3198 ## Summary Change default device identity directory from `.clawdbot` to `.moltbot`. ## The Problem `src/infra/device-identity.ts` hardcodes `.clawdbot/identity` which causes the old directory to be recreated even for users who migrated to `.moltbot`. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates the default device identity storage directory in `src/infra/device-identity.ts` from `~/.clawdbot/identity` to `~/.moltbot/identity`, preventing the legacy `.clawdbot` identity directory from being re-created after users have migrated. The change is localized to the default path constant used by `loadOrCreateDeviceIdentity()`, which is consumed by gateway/client initialization and related tests/helpers when no explicit identity path is provided. <h3>Confidence Score: 4/5</h3> - This PR is low risk and likely safe to merge, with a small behavioral edge case around state-dir overrides. - The change is a single constant update affecting where a file is read/written by default. The main concern is consistency with the repo’s broader state directory resolution (env overrides and legacy/new preference), which could lead to surprising identity location for users who rely on `MOLTBOT_STATE_DIR`/`CLAWDBOT_STATE_DIR` or migration behavior. - src/infra/device-identity.ts <!-- greptile_other_comments_section --> _{(3/5) Reply to the agent's comments like "Can you suggest a fix for this @greptileai?" or ask follow-up questions!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->