docs: remove Bun-runtime callout from remote-shell (post v0.4.0)

[YairEtzion]

Summary

Follow-up to v0.4.0. The prebuilt amesh-agent binaries are live in the GitHub release, the npm postinstall successfully downloads them, and brew install ameshdev/tap/amesh installs both amesh and amesh-agent. This PR updates the /docs/remote-shell and /docs/troubleshooting pages to reflect that reality — the amber "Runtime requirement" callout can come off and the Homebrew / binary install tabs can come back.

End-to-end verification (Docker, before this PR)

Fresh node:20-bookworm-slim container on linux/amd64:

# npm install -g @authmesh/agent@0.4.0
added 48 packages in 13s

# ls -la $(which amesh-agent)
/usr/local/bin/amesh-agent -> ../lib/node_modules/@authmesh/agent/scripts/launcher.mjs

# amesh-agent --version
amesh-agent/0.4.0

# amesh-agent agent start --help
amesh-agent agent start — Start the amesh agent daemon (accepts remote shell connections)
Usage: amesh-agent agent start [flags]
Flags:
  -r, --relay           Relay server URL [default: wss://relay.authmesh.dev/ws]
      --allow-root      Allow running as root ...
      --idle-timeout    Idle session timeout in minutes [default: 30]

The amesh-agent/0.4.0 output format is unique to the compiled sea.ts binary — confirming the postinstall extracted the real binary, not that it fell through to the JS fallback. Nested command dispatch works. No bun wrapper needed.

Changes

landpage/src/routes/docs/remote-shell/+page.svelte

• Homebrew install tab — the server-side command is now brew install ameshdev/tap/amesh (same as the controller). A single tap install puts both binaries in PATH.
• Binary install tab — server-side points at amesh-linux-x64.tar.gz and extracts amesh-agent. The tarballs contain both binaries so the same archive works for both sides.
• Remove the amber Runtime Requirement callout above Setup step 3. It told users to install Bun and wrap with bun $(which amesh-agent) agent start — no longer necessary on supported platforms.
• New Platform Support section with a 5-row table: macOS arm64/x64, Linux x64/arm64, and an armv7 row grayed out with the "Bun wrapper only" caveat. Added to the inline TOC.
• Troubleshooting cards reframed — "Handshake failed" no longer references the Bun wrapper; "requires Bun runtime" is now marked "(armv7 only)" and explicitly notes it should not appear on supported platforms.

landpage/src/routes/docs/troubleshooting/+page.svelte

• Bun runtime entry under Remote shell errors — reframed from "install Bun and wrap" (general) to "this should never appear on supported platforms; if it does, check your postinstall logs for a download failure" (diagnostic). Second paragraph keeps the armv7 guidance.
• Handshake failed entry — drop the Bun wrapper reference.

Test plan

• bun run build (landpage) — clean
• bun run check — 0 errors
• Playwright visual check at 1440px — new Platform Support table renders, callout gone, Setup step 3 clean
• End-to-end: npm install -g @authmesh/agent@0.4.0 in a fresh Linux x64 Docker container, amesh-agent --version and amesh-agent agent start --help work without any wrapper
• CI green on this PR