docs: fix typos, grammar, and broken code snippets in contributor docs

[andromia3]

WHY are these changes introduced?

Cleanup pass on the contributor-facing docs under `docs/cli/`. Every change is either a broken code snippet, an install instruction that doesn't satisfy `package.json#engines`, or a grammar/typo bug. All verified against the current state of the repo.

WHAT is this pull request doing?

Broken code snippets — copy-pasting these would fail:

• `docs/cli/troubleshooting.md` — the Vitest mocking example had `const import {functionA} from 'my-module'`. A `const` before `import` doesn't parse. Dropped the `const`.
• `docs/cli/testing-strategy.md` — the unit-test example binds the result of `load()` to `got` and then asserts on `app.name`, but `app` isn't defined in scope. Changed to `got.name`.

Install instruction below the engine requirement:

• `docs/cli/cross-os-compatibility.md` — the Linux contributor setup installs Node 18 via `curl -fsSL https://deb.nodesource.com/setup_18.x\`. But `packages/cli/package.json` declares `"engines": { "node": ">=20.10.0" }` and `.nvmrc` pins `v24.1.0`. A new contributor following the guide lands on Node 18 and `pnpm install` refuses to run. Bumped to `setup_24.x` to match `.nvmrc`.

Typos, missing words, and agreement bugs:

• `get-started.md` — "might come handy" → "might come in handy"; "all the packagesusing the Typescript `tsc` tool" → "all the packages using the TypeScript `tsc` tool" (missing space + brand casing).
• `conventions.md` — "the name must match the name of the command represent" was missing a word → "…the name of the command it represents"; "spins up an server" → "a server"; the `browser` bullet in the public-modules list was missing its `:` (other bullets in the same list use `- `foo`: For modules…`).
• `architecture.md` — "an horizontally-distributed" → "a horizontally-distributed" (consonant sound); "boundaries that leads" → "boundaries that lead" (plural agreement).
• `performance.md` — "code that don't map 1-to-1" → "code that doesn't map 1-to-1" (singular agreement); "As a last resource" → "As a last resort" (wrong word).
• `testing-strategy.md` — Given/When/Then callout said "blocks, given, when, and using code comments" — "then" was missing; also "the code test" → "the test code"; heading "Github Actions" → "GitHub Actions", plus "marge" → "merge" and another "Github" → "GitHub" in the body.
• `cross-os-compatibility.md` — "standard library work more consistently" → "standard library works" (singular agreement).

How to test your changes?

Docs-only, every change is inside a `docs/cli/*.md` file. Rendering on GitHub or in an editor previewer is enough to verify each fix.

Post-release steps

None.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows) — the `cross-os-compatibility.md` change specifically fixes a Linux-side regression relative to the `engines` field.
• I've considered possible documentation changes — this is the docs change.
• I've considered analytics changes to measure impact — N/A, docs-only.
• The change is user-facing, so I've added a changelog entry with `pnpm changeset add` — `docs/cli/**` is contributor-facing, not user-facing, so no changeset.