Refactor FlashStart

[Tbaile]

The following task will include many sub-issues to help manage the load of the change.

To be added:

• refactor: change implementation from using dnsdist to use dnsmasq, use init.d to handle changes instead of committing them
• support multi profiles using proplus: in case of proplus usage, spin up a DNS server for each proplus instance, every server needs a list of clients assigned at it
• dynamic IP list from flashstart: due to the nature of some blocks, some IPs that need to be filtered are dynamic, fetch the list from upstream and update the firewall (this will have 100% some hiccups due to iplists not updating correctly in some instances of the firewall)
• in light of Allow custom domain resolution settings in Flashstart UI #1098, it's probable that the current resolution of domains using specific DNSs comes keys in hand from the implementation we use to resolve domains.

[cotosso]

The UI needs some little modification to reflect recent changes and support additional configuration parameters.

1. Enable/Disable Toggle

Add a switch to enable or disable the FlashStart filtering service.

2. Service Type Selector (NEW)

Add a dropdown or radio buttons to select the FlashStart service type:

• FlashStart Pro
• FlashStart ProPlus

3. Authentication Section

Add input fields for:

• Username
• Password

4. Filtered Zones

5. Bypass List

Allow specifying IP addresses or networks that should bypass filtering:

• Bypass source IPs or networks

6. Custom DNS for Specific Domains (NEW!)

Add a section to configure custom DNS servers for resolving specific domain names.

Subtitle: Use a specific DNS server to resolve selected domain names instead of the default resolver.
This feature should behave like the "DNS Forwarding Servers" section in the standard DNS configuration.

🔧 Syntax: (to put in the informative blob)

• /<domain>/<server> – Route DNS queries for a specific domain to a custom DNS server.
  Example: /example.com/8.8.8.8

• /<domain>/<server>#<port> – Use this format if the upstream server listens on a non-standard port.
  Example: /example.com/8.8.8.8#5353