fix(repo bootstrap): report a distinct failed state per repository

[Th3Mouk]

Summary

Closes #50.

repo bootstrap always reported a non-skipped repository as executed — in both the human table and the JSON report — even when its bootstrap command exited non-zero. The only signal that anything went wrong lived in the free-text issues[] list, with no structured field on the repository row itself, so the table showed a green "executed" next to a repository whose dependencies were never installed.

This PR is scoped to that specific gap. It intentionally does not change the exit code: report.status still resolves to warning (not error) for a per-repository command failure, and the process still exits 0. That behavior is an existing, documented, and consistently-applied CLI-wide convention — see the "Exit codes" section of docs/cli/commands.md and the 0.2.0 changelog entry that deliberately normalized warning to exit 0 "to match all other commands" (it already applies identically to repo git checkout|pull|sync and worktree remove). Changing that would be a separate, much larger discussion; this PR only fixes the report/table not telling the truth about what happened.

Changes

• BootstrapReport.repositories[] now carries a state of "executed" | "skipped" | "failed" instead of a skipped boolean — mirroring the pattern WorktreeRemoveReport already uses for the same kind of per-repository outcome.
• executeBootstrapPlan now returns which repository names failed (not just a flat issues[] array), so the report can mark the corresponding row failed after execution instead of only ever reflecting the pre-execution plan.
• The human renderer paints failed in red (matching worktree remove's existing tone convention) instead of a misleading green executed, and the summary line now breaks out executed / skipped / failed counts separately.
• Docs: repo bootstrap section now documents the state field and reiterates that a per-repository failure does not affect the exit code, to head off the exact ambiguity reported in repo bootstrap exits 0 when a bootstrap command fails #50.
• Changelog: flagged as BREAKING for JSON consumers reading .data.repositories[].skipped (now .data.repositories[].state === "skipped").

Reproduction

Verified against the exact repro from #50 (a local bare origin, a repository whose bootstrap command does exit 3):

Before:

repo bootstrap: warning (1 executed, 0 skipped, 1 issues)
│ demo │ executed │ sh -c 'echo BOOTSTRAP_RAN; exit 3' │
EXIT=0

After:

repo bootstrap: warning (0 executed, 0 skipped, 1 failed, 1 issues)
│ demo │ failed   │ sh -c 'echo BOOTSTRAP_RAN; exit 3' │
EXIT=0

Test plan

• pnpm build
• pnpm typecheck
• pnpm lint / pnpm format:check
• pnpm test (190/190, including new/updated coverage in bootstrap-execution.test.ts, execution-service.test.ts, and human-renderer.test.ts)
• Manual repro of the exact scenario from repo bootstrap exits 0 when a bootstrap command fails #50, before and after
• pnpm test:audit-prod currently fails on main too (pre-existing shell-quote advisory, unrelated to this change — not touched here)

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