docs: document profiles, new install formats, and the Tauri distribution

[0xbrayo]

Documents features that exist in releases but aren't mentioned in the docs.

getting-started.rst

• Linux: only the .zip was mentioned, but releases (already in v0.13.2) also ship an .AppImage and a .deb. Lists all three with how to use each.
• macOS: notes that v0.14 has separate Apple Silicon (arm64) and Intel (x86_64) downloads.
• Adds a note about the experimental Tauri distribution offered from v0.14 (activitywatch-tauri-*): it replaces aw-qt, embeds aw-server-rust, and bundles awatcher on Linux for Wayland support. The classic distribution stays the default.

faq.rst: the Wayland answer now also suggests the Tauri distribution, alongside switching to X11 or using an alternative watcher.

directories.rst: new Profiles section (v0.14) covering:

• aw-qt --profile <name>, and how the profile reaches the modules through AW_PROFILE (aw-server, aw-server-rust and aw-sync also take --profile)
• the activitywatch-<name> directory roots
• profile name rules (from validate_profile)
• that a named profile needs its own port in its server and aw-client config to avoid colliding with the default instance on 5600

installing-from-source.rst: links to the Profiles section next to the existing --testing explanation.

The v0.14 items describe the current v0.14 betas; v0.13.2 is still the latest stable release. Built locally with Sphinx with no new warnings, and merges cleanly alongside #194–#197.