falter-bird-utils: add UCI-to-Bird2 configuration translator

[adityachooramani]

Pull Request Submission
Compile tested: No (Architecture-independent shell scripts and UCI configuration) Run tested: Yes.

Arch: x86_64

Model: QEMU VM

Falter Version: Snapshot (Dec 2025)

Tests done: 1. Verified procd triggers: uci commit successfully triggers config regeneration and bird reload. 2. Verified Dynamic ID: Logic successfully pulled the br-lan IP (192.168.42.1) for the router id. 3. Verified Syntax: bird -p -c /var/etc/bird.conf returns no errors. 4. Verified Filters: UCI import_filter and export_filter options correctly map to Bird2 protocol channels.

Description of the changes: This PR introduces the falter-bird-utils package, a dedicated UCI-to-Bird2 translator. It is designed to modernize how Bird2 is handled on Falter nodes by moving away from static files toward a dynamic, UCI-driven approach.

Key Features:

Automated Logic: Uses an init script with procd integration to handle lifecycle and configuration generation.

Hardware Friendly: Writes the generated bird.conf to /var/etc (RAM) to prevent unnecessary flash wear.

Intelligent Discovery: Includes a BusyBox-compliant pipeline to automatically detect the node's primary IPv4 for the BGP router id.

Bird 2.x Syntax: Specifically handles the local as and ipv6 { channel } syntax requirements of modern Bird versions.

[akira25]

@adityachooramani please do never merge the main branch into a feature branch. Please rebase instead: https://git-scm.com/book/en/v2/Git-Branching-Rebasing

[akira25]

I'm not an expert for bird2, thus you should get a detailed review from another person. I have two remarks though from skimming your code:

1. You set r_id=1.1.1.1 as a default, when you can not detect another gloabl IP-Address. I know, that most of the internet uses cloudflare and doesn't care, but at freifunk, we see monopolies a bit critical. It would be better, to make that configurable somehow. A good alternative (at least for people located in europe) is Quad9, whichs uncensored Service is a 9.9.9.10
2. What does your software do, when there is no IPv4 address? Many freifunk communities do IPv6-only already. Your software should be IP-Version agnostic, if possible.