Replaces the cluster_config->port fallback (dead after task 1.2) with:
--peers candidate match (unchanged, including single self-referencing
entries for a custom single-node port) -> hardcoded XCE_CONTROLLER_DEFAULT_PORT
(9990) when --peers was never passed at all. The --peers-given-but-local-
name-absent case still returns -EINVAL and refuses to start, unchanged.
Also folds in task 1.3's discovery (HashZArrayConfig/ResmgrConfig capnp
structs left orphaned by tasks 1.1/1.2, breaking codegen) into
requirements.md (new Req 2.5)/design.md/research.md/tasks.md, and fixes
a design.md citation error (validate_peer_count -> xce_parse_peers) found
during task 2.1's review.
Removes port, candidates, vcpus, jobmgr, workermgr, qmgr, resmgr, xstrings
from the ClusterConfig capnp struct plus the now-unused MasterCandidate
struct, per the config-design.md shared-vs-local classification rule.
Cap'n Proto forbids ordinal gaps, so the 13 retained fields are renumbered
to a contiguous @0..@12 (accepted pre-1.0 wire-compat break — see
research.md's "Design Revision 2"). requirements.md/design.md updated to
match: Req 3.1 drops field-number invariance, Req 3.2/4.1 state a pre-spec
cluster.bin is not expected to decode correctly, and a new Req 5.3 covers
regenerating the checked-in ha/data/cluster.bin fixture in a later task.
Also folds in this session's live design revision: Requirement 1.7's port
replacement mechanism is the existing --peers self-reference + a hardcoded
default (no new --port CLI flag), confirmed via interactive review with
the spec owner.
