Add agentpr and watchpr CLI tools

agentpr manages PRs/comments/whoami as unkin-agent (Vault AppRole -> gitea creds
-> Gitea API), fixing tea's post-as-Ben default. watchpr polls PRs and alerts
only on merge/close, human comment, CI failure, or lost mergeability.

- cobra multi-binary layout mirroring node-lookup (cmd/ + internal/)
- Makefile (build, patch|minor|major, completions, rpm), nfpm RPM with both
  binaries + bash/zsh/fish completions, woodpecker CI publishing to rpm-internal
- unit tests for parsing, meaningful-change detection, and the Vault+Gitea client

go.mod

@@ -0,0 +1,10 @@
+module git.unkin.net/unkin/agent-tools
+
+go 1.26.5
+
+require github.com/spf13/cobra v1.10.2
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+)