fix(omo-senpi): point the local launcher update hint at bun - #8895

Refs code-yeongyu/senpi#2157 (tracking issue; senpi side is code-yeongyu/senpi#2158)

What changed

The generated local omo launcher (packages/omo-senpi/src/install/local-launcher.ts, written by oh-my-openagent install for a local sibling-store checkout) answered omo update with omo is updated via npm: npm i -g omo-ai[@beta] and carried that npm command as the brand update.command. It was the last surface still steering users to an npm install of omo-ai. It now prints omo is updated via bun: bun add -g omo-ai[@beta] and carries the bun command. plugin/scripts/install.mjs is regenerated with node packages/omo-senpi/plugin/scripts/build-install.mjs (4-line diff, same as the source change).

Not changed on purpose: the published launcher (omo-native/bin/lib/package-paths.js) already answers with the manager that installed omo-ai (npm i -g for npm installs, bun add -g for bun installs); switching an npm install's update command to bun would create a second, shadowing install.

Why

senpi#2157 makes the engine recommend a clean reinstall with Bun when it runs on Node.js. Every omo install instruction (README, install guide, release notes, package description) is already Bun-first; this aligns the one remaining hint.

QA & Evidence

• WHAT WAS TESTED: installLocalLauncher(...) into a temp HOME for a prerelease (5.0.0-0.beta.90) and a stable (5.0.0) version, then the real generated launcher run as node <tmp-home>/.local/bin/omo update.
• WHAT WAS OBSERVED: exit 0 and omo is updated via bun: bun add -g omo-ai@beta (prerelease) / omo is updated via bun: bun add -g omo-ai (stable); temp HOME removed afterwards. Evidence: .omo/evidence/omo-senpi-adapter/20260927-local-launcher-bun-update/launcher-update.json (local, not committed), sha256 a11b1a616e14f5874e599b58e6e9683417742b032696922a900f91cea0c33eda.
• Gates: bun test packages/omo-senpi/src/install/local-launcher.test.ts packages/omo-senpi/src/install/install-senpi-launcher.test.ts 10 pass / 0 fail; tsgo --noEmit -p packages/omo-senpi/tsconfig.json exit 0.
• WHY IT IS ENOUGH: the change is the rendered launcher's update string and brand command; the launcher tests parse the rendered brand JSON and the printed hint, and the live run exercises the generated file.
• WHAT WAS OMITTED: no live session was needed (no engine/extension behavior changed); no secrets involved.

Summary by cubic

The local omo launcher now tells users to update with bun instead of npm, matching the README, the install guide, and senpi's Node.js runtime notice.

• The generated launcher for local sibling-store installs answered omo update with npm i -g omo-ai[@beta]; it now prints bun add -g omo-ai[@beta] and carries that as the brand update.command.
• The published launcher (omo-native/bin/lib/package-paths.js) is left alone since it already answers with the manager that installed omo-ai, and switching an npm install to bun would create a shadowing second install.
• plugin/scripts/install.mjs is regenerated from the source; CHANGELOG and changes.md updated.

^{Written for commit 0f4544e. Summary will update on new commits.}