fix: add config migration for `[stats]` section and bump to `0.2.1` (#…

…116)

v0.2.0 shipped the required [stats] config field without migration
logic, so any pre-existing clawshell.toml fails to parse on upgrade.

- New to_v0_2_1 migration step injects [stats] with persist_path =
  "/etc/clawshell/stats.json" when the section is absent.
- Version gate (from < 0.2.1) catches both 0.1.x and 0.2.0 configs.
- Bump version to 0.2.1 across Cargo.toml, example config, README,
  and all npm packages.

chore: bump version from `0.1.1` to `0.2.0` (#115)

chore: bump version from `0.1.0` to `0.1.1` (#68)

The `0.1.0` version was accidentally released in npm, so we have to use another version.

chore: bump version from `0.1.0-alpha.1` to `0.1.0` (#67)

chore: bump version from `0.1.0-alpha.0` to `0.1.0-alpha.1` (#64)

feat(migration): support the pre-release version like `0.1.0-alpha.0` (…

…#59)

docs: fix build status badge link in README (#2)