Remove pr-finish from self-development skills

[gjkim42]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

The shared self-development AgentConfig installed the entire
gjkim42/kanon-repo skills package, which also made pr-finish available to
every self-development agent.

This PR replaces the package-wide installation with an explicit allowlist of
the five intended shared skills, leaving out pr-finish. It also updates the
self-development documentation and updater prompts to preserve individual
skill selection, and updates the manifest test to enforce the allowlist.

Which issue(s) this PR is related to:

N/A

Special notes for your reviewer:

Validation:

• make verify
• make test TEST_FLAGS='-run TestSelfDevelopment'

The full make test run reached two unrelated Codex entrypoint test failures:
TestCodexEntrypointUsesPersistentSessionHome and the Codex case of
TestAgentEntrypointsPreserveSkillReferenceFiles. The changed
self-development tests pass.

Does this PR introduce a user-facing change?

NONE

---

Summary by cubic

Replaced the package-wide install of gjkim42/kanon-repo skills with an explicit allowlist to remove pr-finish from self-development agents. Updated docs and tests to reflect and enforce individual skill selection.

• Refactors
  • base-agent.yaml now installs five skills explicitly: api-review, design-cleanup, gjkim-instruction, pre-session-end, review-all.
  • Updated README and updater prompts to reference selected shared skills instead of the full package.
  • Updated the self-development test to assert the exact allowlisted skills.

^{Written for commit 0839fbc. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 5 files

_{Re-trigger cubic}