fix: format IPv6 endpoints for integrations

[frahlg]

Summary

• Format CTEK and Nova endpoint addresses with net.JoinHostPort after removing brackets only from valid IPv6 literal host parts.
• Encode raw IPv6 zone IDs as %25 in Nova broker URLs, while preserving already encoded %25 without double-escaping.
• Keep IPv4, hostnames, and Nova diagnostic address semantics unchanged.
• Keep the existing driver-fingerprint path unchanged; its input normalization already handles bracketed IPv6.
• Add table-driven regressions for IPv4, hostnames, bare/bracketed IPv6, and raw/already-encoded zone IDs.
• Keep the patch changeset.

Why

Issue #725 identifies malformed host:port strings for bare IPv6 literals. The independent review of #786 also found that already bracketed input became [[fd00::5]], and that Nova broker URLs rejected raw IPv6 zone IDs such as fe80::5%en0. Nova URL zone IDs now follow RFC 6874.

Scope and non-overlap

• This is the mechanical, low-risk slice of IPv6: dual-stack works, but IPv6 literals break outbound paths and discovery is IPv4-only #725.
• It does not change API authentication, Home Link, Site Companion access, or any write permission.
• fix(api): require auth for sensitive reads #744 remains the owner of sensitive API-read protection; security.go is untouched.
• Define the read-only Site Companion access contract #624 remains a contract/design boundary; no Site Companion route or new grant is added.
• MQTT/HA driver dial paths and go/internal/drivers/registry.go remain outside this PR and their existing owners.

Checks

Passed locally on eebe93e3, rebased on live master 6d4b958a7e29b52fac69b4c919f99e4409c41348:

• make verify
• pre-commit make verify
• pre-push make verify-all (including Linux arm64/amd64 and Windows amd64 cross-builds)
• targeted go test ./internal/api ./internal/evcloud ./internal/nova -count=1

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Encode raw zone IDs that begin with 25

When the raw IPv6 zone itself starts with 25 (for example, the common numeric interface index in fe80::5%25), this prefix check mistakes it for an already URL-encoded delimiter and returns ssl://[fe80::5%25]:8883. url.Parse, as used by Paho's AddBroker, decodes that host to [fe80::5%]:8883, which cannot be resolved, so Nova never connects on that interface. The input representation must be canonicalized or otherwise disambiguated rather than treating every %25... suffix as pre-encoded.

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