Fix manifest bot_user, drop Gemini extension, consolidate skill install on npx

[howar31]

Surfaced during hands-on UX validation of the install/onboarding flow.

Changes

• fix(manifest): declare features.bot_user in the generated app manifest. Slack's "create app from manifest" form rejects bot scopes without a bot user (Oauth requires bot_user); this unblocks app creation.
• chore: remove the Gemini extension distribution channel. gemini-extension.json only set contextFileName to the index skill — npx skills natively targets gemini-cli, so the bespoke extension is redundant. Also dropped from the VERSION fan-out (sync-version.sh, CI version-sync).
• docs: make npx skills the primary agent-skill install path; fold OpenClaw in, drop the unverified OpenClaw binary-autoinstall claim, and defer install/update behavior to the npx skills wizard.

Verification

• go test ./... green; skill / manifest / version-sync CI drift guards all pass locally.
• Agent-side runtime check: read + write (user and bot tokens) exercised against a live workspace.

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request removes the gemini-extension.json file and updates the versioning and documentation workflows accordingly. It also modifies the manifest generation logic to automatically include a bot_user feature when bot scopes are present, ensuring compatibility with Slack's app creation requirements. Feedback was provided to improve the readability of the manifest generation code by pre-calculating scope sets and ensuring consistent JSON schema output.

[gemini-code-assist]

For better consistency and readability, consider calculating both userScopes and botScopes before initializing the manifest map. This makes the map literal cleaner and ensures both scope sets are handled identically. Additionally, ensure that the generated manifest maintains a consistent schema even if these scope lists are empty, as per repository standards for command outputs.

	userScopes := scopeUnion(root, "user")
	botScopes := scopeUnion(root, "bot")
	manifest := map[string]any{
		"display_information": map[string]any{"name": "slk"},
		"oauth_config": map[string]any{
			"scopes": scopes{User: userScopes, Bot: botScopes},
		},

References

1. Ensure JSON output for commands maintains a consistent schema even when data lists are empty. Standard envelope or metadata fields should be included alongside empty arrays to ensure a predictable structure for programmatic callers.