Land remaining unmerged branches

[jasonsuhari]

Problem: the repository has many leftover local and remote branch tips and open PRs that are not yet on main.\n\nRequested behavior: merge the remaining useful branch work into main, validate the integrated result, and clean up related leftover branches/worktrees where safe.\n\nAcceptance checks:\n- Remaining open PR branch work is represented on main or a blocker is reported.\n- Relevant validation passes on the integrated result.\n- Local main is fast-forwarded to origin/main after merge.\n- Related stale branches/worktrees are cleaned up when safe, with any remaining ambiguous work reported.

[jasonsuhari]

Final cleanup pass: PR #113 is merged into main, the integration commit is on origin/main, validation passed from local main, the installed gridbash binary hash matches the rebuilt binary, superseded PRs were closed, stale remote branches were deleted, and 50 clean stale worktrees were removed. Remaining local-only cleanup is blocked on dirty worktrees with unresolved/uncommitted files, so they were left in place rather than discarded: chore-finish-remaining-agent-merges, chore-land-useful-feature-branches, feat-integrate-dedicated-command-line, feat-integrate-resume-sessions, feat-tabs, and tmp-merge-green-check.