Opt /do into UI screenshot evidence on PRs (#749)

**Kolu now opts into [`/do`](https://github.com/srid/agency)'s
`evidence` step**, so every PR that touches the UI ends up with
before/after screenshots posted under an `## Evidence` heading. The
instruction file at `.apm/instructions/pr-evidence.instructions.md`
tells the agent how to drive the chrome-devtools MCP, and the agency dep
is refreshed (`96994aff` → `c122f08e`) so the new opt-in plumbing is
actually present.

The capture flow leans on infra Kolu already has: `just dev` for the
live app, the `chrome-devtools` MCP wired through `just
ai::mcp-chrome-devtools`, and `gh release upload` to a long-lived
`evidence-assets` release for hosting — _PR comments can't attach
binaries, so the release acts as a stable CDN that doesn't pollute git
history_. Server-only / docs / Nix-only diffs short-circuit with a
one-line "no UI changes" comment, so the step stays cheap when there's
nothing visual to show.

Most of the diff is regenerated `.claude/`, `.codex/`, `.opencode/`, and
root/per-package `AGENTS.md` output from `apm install` + `apm compile -t
codex,opencode`. The only hand-written source is the new instruction
file.

_Generated by Claude Code (model \`claude-opus-4-7\`)._