§H.12 steps 5-6: pin Hera/Hermes/Artemis in generic capsule-birth admission

capsule_birth.c's generic admission block now registers a session for
every born VM (session_register) and pins it (session_set_pinned) when
the birthing capsule is Hera/Hermes/Artemis.

Bug found and fixed via a temporary probe (written, run, captured,
reverted): the fleet-foundation name check first used an exact-match
comparison against "Hermes"/"Artemis", but capsule_name is actually
"hermes:init.4th"/"artemis:init.4th" (the real namespace:filename
convention) -- the check silently never matched, both would-be-pinned
VMs stayed unpinned. Fixed with a new vm_name_prefix_eq_nocase() helper
matching everything before a literal ':'. Probe confirmed pinned=0 before
the fix, pinned=1 after, on all relevant VMs.

Session.parent is hardcoded to vm_uuid_hera() for now (every birth
through this path is Hera-initiated today); step 7 generalizes this to
the actual birthing VM's own id.

Verified 3-arch boot to ok> (amd64/aarch64/riscv64) on the final,
probe-free code.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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