feat(server-ng): add cluster.nodes.advertised_address for clients

[mmodzelewski]

A node's ip is the address it binds for replica traffic, which in
Docker, Kubernetes, or NAT deployments is private. Both client-facing
surfaces reuse it: the cluster roster returned to clients and the
follower's redirect to the metadata primary. Clients outside the
replica network get an address they cannot reach.

Nodes now take an optional advertised_address that overrides ip
only where an address is handed to a client. Replica traffic still
uses ip, so the two planes can live on separate networks. Left
unset, behavior is unchanged.

The value parses into an AdvertisedAddress: a literal IP or an
RFC 1123 hostname, rejecting ports, empty labels, and dotted-numeric
strings that are really malformed IPv4, so 10.0.0.256 fails at boot
instead of reaching DNS. Hostnames normalize to lowercase and IPs to
canonical form, so textual variants of one address compare equal and
publish identically; IPv6 hosts are bracketed when rendered with a
port.

Validation now also checks advertised client endpoints for conflicts
alongside the existing bind-endpoint check, since two nodes on
distinct private IPs can otherwise publish the same client address
and silently shadow each other. Only client transports take part,
as replica ports never carry an advertised address. A roster ip
that parses as neither IP nor hostname stays legal (Docker service
names with underscores exist in the wild) and falls back to
raw-string comparison instead of failing boot.

Node entries also reject unknown fields, so a misspelled
advertised_address fails at startup instead of silently leaving the
private ip in client responses.

[codecov]

Codecov Report

❌ Patch coverage is 98.35165% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.55%. Comparing base (ab944b5) to head (ac11d63).

Files with missing lines	Patch %	Lines
core/configs/src/server_ng_config/cluster.rs	98.91%	3 Missing ⚠️
core/server-ng/src/http/error.rs	92.30%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3757       +/-   ##
=============================================
- Coverage     74.58%   60.55%   -14.04%     
  Complexity      969      969               
=============================================
  Files          1306     1305        -1     
  Lines        150282   138231    -12051     
  Branches     125715   113738    -11977     
=============================================
- Hits         112088    83703    -28385     
- Misses        34690    50941    +16251     
- Partials       3504     3587       +83     

Components	Coverage Δ
Rust Core	57.75% <98.35%> (-17.15%)	⬇️
Java SDK	62.71% <ø> (ø)
C# SDK	71.13% <ø> (-1.13%)	⬇️
Python SDK	92.27% <ø> (ø)
PHP SDK	84.52% <ø> (ø)
Node SDK	92.24% <ø> (+0.12%)	⬆️
Go SDK	43.08% <ø> (ø)

Files with missing lines	Coverage Δ
core/configs/src/server_ng_config/defaults.rs	100.00% <100.00%> (ø)
core/configs/src/server_ng_config/validators.rs	78.93% <100.00%> (+0.06%)	⬆️
core/server-ng/src/bootstrap.rs	16.02% <100.00%> (+0.04%)	⬆️
core/server-ng/src/cluster_meta.rs	77.77% <100.00%> (+61.90%)	⬆️
core/configs/src/server_ng_config/cluster.rs	96.74% <98.91%> (+1.88%)	⬆️
core/server-ng/src/http/error.rs	56.88% <92.30%> (+5.43%)	⬆️

... and 261 files with indirect coverage changes

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