[Fix] Create Slack app button hard to see when disabled

[roomote-roomote]

Opened on behalf of Matt Rubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

Related issue

N/A — internal fix from Slack feedback on Create Slack app button visibility.

Why this PR exists

• A maintainer explicitly invited this PR in the linked issue or discussion
• I am a maintainer / this is internal Roomote work

What changed

Disabled primary buttons used foreground/5 for both background and text, so labels like Create Slack app were nearly invisible on the lime setup surface until a token was entered.

Disabled default, destructive, secondary, and outline button styles now use stronger disabled contrast (foreground/40 text, slightly stronger fill/border) while remaining clearly inactive.

Why this change was made

On self-hosted setup the Create Slack app control is correctly disabled with an empty token, but the old ultra-faint disabled styling made it look broken rather than waiting for input. This was not a light/dark mode bug — setup already forces light mode.

Impact

Users can still tell the button is disabled, but the label stays readable on light and high-chroma surfaces (including setup). Enabled button styling is unchanged.

How it was tested

• pnpm exec dotenvx run -f .env.test -- pnpm --filter @roomote/web exec vitest run src/components/system/primitives/button.test.tsx
• Pre-push suite: oxlint, residual lint, check-types:fast, knip
• Manual browser screenshots of Create Slack app disabled and enabled states in Settings → Communications

Screenshots

Checklist

• The PR title follows the repo convention: [Fix], [Feat], [Improve], [Refactor], [Docs], or [Chore] followed by a user-facing description
• This PR is small and scoped to one change
• pnpm lint and pnpm check-types pass locally
• I added tests or included a clear manual validation note above
• I removed secrets, tokens, private keys, and customer data from code, logs, and screenshots
• If this change should appear in the changelog, I ran pnpm changeset

[roomote-roomote]

No code issues found. See task

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