chore: remove tor from startos core

Tor is being moved from a built-in OS feature to a service. This removes
the Arti-based Tor client, onion address management, hidden service
creation, and all related code from the core backend, frontend, and SDK.

- Delete core/src/net/tor/ module (~2060 lines)
- Remove OnionAddress, TorSecretKey, TorController from all consumers
- Remove HostnameInfo::Onion and HostAddress::Onion variants
- Remove onion CRUD RPC endpoints and tor subcommand
- Remove tor key handling from account and backup/restore
- Remove ~12 tor-related Cargo dependencies (arti-client, torut, etc.)
- Remove tor UI components, API methods, mock data, and routes
- Remove OnionHostname and tor patterns/regexes from SDK
- Add v0_4_0_alpha_20 database migration to strip onion data
- Bump version to 0.4.0-alpha.20

sdk/base/lib/util/patterns.ts

@@ -21,11 +21,6 @@ export const localHostname: Pattern = {
   description: 'Must be a valid ".local" hostname',
 }
 
-export const torHostname: Pattern = {
-  regex: regexes.torHostname.matches(),
-  description: 'Must be a valid Tor (".onion") hostname',
-}
-
 export const url: Pattern = {
   regex: regexes.url.matches(),
   description: 'Must be a valid URL',
@@ -36,11 +31,6 @@ export const localUrl: Pattern = {
   description: 'Must be a valid ".local" URL',
 }
 
-export const torUrl: Pattern = {
-  regex: regexes.torUrl.matches(),
-  description: 'Must be a valid Tor (".onion") URL',
-}
-
 export const ascii: Pattern = {
   regex: regexes.ascii.matches(),
   description: