docs: normalize clone URL and package manager to repo's current shape

[Chen17-sq]

Linked issue

Closes #135.

Summary

Several user-facing docs still tell readers to git clone ekailabs/ekai-gateway and run npm install, while CONTRIBUTING.md documents a pnpm workspace flow. The repo's canonical name is now ekailabs/contexto; this PR updates the docs to match without touching anything the issue called out as out-of-scope.

Changes

File	What changed
docs/getting-started.md	clone URL → contexto, cd ekai-gateway → cd contexto, npm install/npm run build/npm start → pnpm equivalents
docs/USAGE_WITH_CLAUDE_CODE.md	clone URL + cd + 2× npm → pnpm (incl. troubleshooting line)
docs/USAGE_WITH_CODEX.md	clone URL + cd + 2× npm → pnpm (incl. troubleshooting line)
docs/ROFL_DEPLOYMENT.md	clone URL + cd
docs/intro.md	GitHub badge points at ekailabs/contexto (URL + label)
docs/memory-plugin.md	npm install @ekai/memory → pnpm add @ekai/memory; npm run start -w @ekai/memory → pnpm --filter @ekai/memory run start

Diff: 6 files, +20/-20.

Intentionally left as-is

Per the "Out of scope" section of issue #135:

• "Ekai Gateway" product name in prose (e.g. docs/USAGE_WITH_CODEX.md:3, docs/ROFL_DEPLOYMENT.md:3, docs/USAGE_WITH_CLAUDE_CODE.md:3,40)
• ekai-gateway-runtime Docker compose stage name (docs/getting-started.md:66)
• ghcr.io/ekailabs/ekai-gateway published image and local Docker tag references
• The @ekai/memory package name (it's a package import, not a repo path)
• Root package.json is still named ekai-gateway — out of scope per the issue ("worth a separate ticket")

Verification

# Confirm no `npm install / npm run / npm add / ekailabs/ekai-gateway` strings
# remain in the touched docs (word-boundary regex to avoid matching `pnpm`):
$ grep -nE '(^|[^p])npm install|(^|[^p])npm run|(^|[^p])npm add|ekailabs/ekai-gateway' \
    docs/getting-started.md docs/USAGE_WITH_CODEX.md docs/USAGE_WITH_CLAUDE_CODE.md \
    docs/ROFL_DEPLOYMENT.md docs/intro.md docs/memory-plugin.md | grep -v '@ekai/memory'
# (empty — clean)

# Remaining `ekai-gateway` mentions are exactly the prose / compose-stage refs
# the issue listed as out-of-scope.