[deploy] #3 BIRD iBGP-snippet generator

[vxfemboy]

M0 (#166). blackwalld emits the iBGP protocol block + egress export-filter from its own config, so prefix/tenant lists aren't maintained in both blackwall and bird.conf.
Status: NONE · Size: M · Home: blackwall-bgp/config + deploy bird/ tree.
Pro: one source of truth; reuses the existing RTD_BLACKHOLE plumbing. Con: must fit the hand-maintained bird.conf/egress.conf layout. Needs its own spec→plan.

[vxfemboy]

Shipped via PR #188 (BIRD iBGP-snippet generator: render_bird_ibgp + bird-config CLI + real-BIRD2 lab gate).