feat(bot): team chat keepalive every 5 minutes, and fix the linux CI build

[3vcloud]

Two commits.

feat(bot): send a team chat keepalive every 5 minutes

The party search bots only ever listen - they never send anything to the game
server - so the game was kicking them for being idle. Send ping on the team
channel every 5 minutes from the main bot loop, just after
ensure_correct_outpost() so it only fires once we're in-game and settled. The
bots are their own one-man party, so no other player sees it. Same trick
kamadanv2's trade bot already uses (main.c:976).

ci: fix the linux bot build

Build bot on alpine has been red on master for over a year, for three
independent reasons:

• It never ran Headquarter's bootstrap.py, so mbedtls and curl were never
  built and cmake died on find_package(MbedTLS). Now bootstrapped with
  CFLAGS=-fPIC, since mbedtls is linked into the bot's shared library.
• It built on Alpine, but Headquarter's linux/thread.c assumes pthread_t is
  an integer, which only holds on glibc (-Werror=int-conversion on musl).
  Builds on debian:bookworm-slim now - the same toolchain the deployed
  partysearchbot image uses.
• main.cpp couldn't compile against the C headers at all: event.h declares a
  struct member named friend, and Headquarter defines a noreturn macro that
  mangles libstdc++'s [[gnu::noreturn]]. Both are handled around the
  extern "C" block now, instead of relying on the sed hacks in
  gwdevhub-core's deployment Dockerfile.

Workflow file renamed bot_alpine.yaml -> bot_linux.yaml since it's no longer
alpine. Verified green in CI (1m05s), and I also re-ran the gwdevhub-core
deployment Dockerfile build against this branch - still builds, the seds there
are now no-ops but harmless.

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