prosody: update to 13.0.6

prosody: update to 13.0.6

0.12.x is EOL upstream and accumulating CVEs. Bump to the current
stable 13.0.6, which carries the fix from security advisory
2026-04-29 / prosody.im/security/advisory_735dd9d3 that first shipped
in 13.0.5.

Prosody 13 requires Lua >= 5.2 (configure rejects 5.1). Switch the
build and runtime to Lua 5.4 and depend on the new
luafilesystem5.4 / luaexpat5.4 / luasec5.4 / luasocket5.4 variants.
Drop the now-unused luabitop dependency: bit operations are built in
since Lua 5.3.

Other notes:
- configure now needs an explicit --lua-version=5.4 and --runwith=lua5.4
  because the wrapper script defaults to '/usr/bin/lua' (5.1 on OpenWrt).
- Install the new mod_debug_stanzas plugin directory. The commented-out
  fallbacks/*.lua install is dropped rather than revived: upstream's
  'make install' never copies that directory, and fallbacks/lxp.lua is
  Lua 5.1 code using module(), which does not even load on 5.4.
- util-src/hashes.c now calls EVP_blake2{s256,b512}(), which libopenssl
  does not provide unless OPENSSL_WITH_BLAKE2 is set, so compile those
  two hashes out when libcrypto lacks them. Selecting the symbol instead
  is not enough: the resulting util/hashes.so still fails to relocate
  against a stock libcrypto, and prosody aborts at startup. Only the
  COMPAT util.hmac table references them, and it tolerates nil entries.
- Install loader.lua. 13.x moved every internal require() to the
  'prosody.*' namespace, and loader.lua is what maps those names back
  onto the installed layout. It is the first file prosodyctl looks for,
  so both prosody and prosodyctl abort at startup without it.

Refs: https://github.com/openwrt/packages/issues/29252
Release notes: https://blog.prosody.im/prosody-13.0.6-released/
Security: https://prosody.im/security/advisory_735dd9d3/

Signed-off-by: Alexandru Ardelean <redacted>