chore: add lefthook config, mise-bump workflow, update README

[brucearctor]

Summary

Developer experience improvements: opt-in git hooks, automated tool version bumping, and updated onboarding docs.

PR 3 of 3 — independent, can merge in any order. See #1383 for the full effort.

Changes

lefthook.yml (new, opt-in only)

• pre-commit: cargo +nightly fmt --all -- --check
• pre-push: cargo lint + cargo check

Not auto-installed. Developers opt in:

brew install lefthook   # or: mise use lefthook
lefthook install

.github/workflows/mise-bump.yml (new)

Weekly scheduled workflow (Monday 9am UTC):

1. Runs mise outdated to detect new tool versions
2. Runs mise up --bump if updates exist
3. Opens a PR via peter-evans/create-pull-request

Complements existing dependabot config (which does not support mise.toml).

README.md

• Replace manual protoc install instructions with mise install
• Add optional lefthook opt-in section

Ref #1383

[chris-olszewski]

Talked a bit about it with the team and we're pretty set on not wanting a tool config checked in that isn't necessary for development.

I also want to hold off on autobumping mise tooling until we see it become an actual issue.

[brucearctor]

@chris-olszewski

I am not invested in lefthook specifically, it would help me [ and I imagine others ] if there is a semi-opionionated/opt-in way to handle that form of automation. I thought about keeping local, but imagined a similar comment of not desired if adding lefthook.yml [ or precommit.yml, ol prek ] to .gitignore at least.

Ex: i forget to run lint, other things for pre-commit and/or prepush. Please have a guide published for the reccommendation, if this PR isn't the solution? Since I can't get fast-feedback from CI [ have to wait for someone on the temporal team to run CI -- that is a waste of a feedback cycle -- how can we solve for this? What are you, others doing for git hooks [ or instead of ]?