* fix(agent): disable seahorse context manager on freebsd/arm
Exclude freebsd/arm from the seahorse-enabled build and route it to the
unsupported stub implementation.
This avoids freebsd/arm build failures caused by modernc sqlite/libc while
keeping picoclaw buildable on that target.
* build: bump Go version from 1.25.8 to 1.25.9
* ci: install and run govulncheck directly in PR workflow
- add build tags to exclude context_seahorse.go on mipsle and netbsd
- add context_seahorse_unsupported.go to keep registration and return a clear runtime error
- remove unused indirect dependency github.com/reiver/go-porterstemmer from go.mod and go.sum
wenjie