Enable full IPv6 support across Pulse probes (ICMP, TCP, HTTP)

[abishekve]

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Title: Enable full IPv6 support across Pulse probes (ICMP, TCP, HTTP)

Description:
Currently, Pulse only supports probing IPv4 hosts. This change enables admins to configure and monitor IPv6-only or dual-stack endpoints via YAML config.

Scope of Work:

• YAML Schema: Update config.schema.json to validate IPv6 addresses (regex exists – confirm and test).

• EF Core Entity: Endpoint.Host supports 253 chars, sufficient for IPv6; validate storage/indexing.

• Probe Drivers:

  • ICMP probe: add IPv6 ping support.
  • TCP probe: allow IPv6 sockets (AF_INET6).
  • HTTP probe: ensure DNS resolution includes AAAA records.

• Tests:

  • ICMP ping to IPv6-only test host.
  • TCP connect to IPv6 service.
  • HTTP GET via IPv6 address.

• UI & Examples: Update YAML examples to include IPv6 targets.

• Verify rollup and outage detection continue to work unchanged.

Acceptance Criteria:

• Admin can add an IPv6 host in YAML config and Pulse successfully probes it.
• Live board shows status for IPv6 endpoints like IPv4.
• Error handling distinguishes "host unreachable (IPv6)" vs "host unreachable (IPv4)".
• Semaphores / batching logic work for IPv6 endpoints.
• Automated tests cover ICMP, TCP, and HTTP over IPv6.
• CIDR safety: IPv6 CIDR expansion blocked by default for prefixes < /120.
• Logs provide clear messages: “IPv6 probe attempt failed — OS fell back to IPv4”.

Developer Notes:

• PR / Branch: [#161](feat: enable full IPv6 support for ICMP, TCP, and HTTP probes #161)
• Zone/Scope Handling: Link-local addresses (fe80::/10) may include a zone/index (e.g., fe80::1%eth0) to disambiguate multiple interfaces.

Tests Added / Updated:

• ConfigurationValidationTests [updated]
• ProbeService tests [added]

Discussions:

• IPv4 | IPv6 | Dual option for HTTP ping handled by DNS provider.