ci: run GitHub Actions on self-hosted runners

[danievanzyl]

Closes #103

Validation

shepard-tests: DISCOVERED=4 RAN=4 PASS=4 FAIL=0 sha=e2058f4 ASSERTIONS=62 APASS=62 AFAIL=0

Ledger diff against PR base 126669227e6e56c740ea18c04a0b6a80f601278e, produced with scripts/run-tests.sh --ledger <path>:

• New FAIL records: 0
• TEST records with decreased assertion counts: 0

Also validated all workflow YAML parses and no runs-on: ubuntu-latest remains under .github/workflows/.

[danievanzyl]

Review — BLOCKED-needs-human

• [BLOCKER] Required PR feedback loop is red on the self-hosted runner. test fails because jq is absent; this also makes code-reviewer-push.sh select the wrong directory and fail its push assertion. The runner must be provisioned with jq because locked intent forbids changing workflow steps.
• [BLOCKER] validate reaches the regression suite but fails the pre-existing assertion keeps extension-provided runtime support available to existing personas: extensions/subagents/index.ts always adds --no-extensions, while the base test expects it omitted for an extension-provided model. This is unchanged from resolved base 126669227e6e56c740ea18c04a0b6a80f601278e; fixing it here would violate the no-unrelated-diff requirement.
• [INFO] The PR diff itself matches ci: run GitHub Actions on self-hosted runners #103 exactly: only the four named workflows changed; each change is solely ubuntu-latest → self-hosted; no old label remains; YAML parses; triggers, permissions, steps, and other bytes are unchanged.
• [INFO] PR body contains the verbatim head summary: shepard-tests: DISCOVERED=4 RAN=4 PASS=4 FAIL=0 sha=e2058f4 ASSERTIONS=62 APASS=62 AFAIL=0. Independent base/head ledger runs found 0 new FAIL records and 0 decreased assertion counts.

No review commits: the implementation needs no in-scope code correction. Human action is required to provision the runner and resolve/waive the unrelated baseline regression before the mandatory feedback loop can pass.

[danievanzyl]

Verdict: CLEAN

No collateral regressions found across the four changed workflow-job surfaces.

shepard-survey: SURFACES=4 PROBED=4 FINDINGS=0 sha=e2058f4