fix: harden snapshot validation and spice handling

[TimInTech]

Summary

• align snapshot name validation with Proxmox rules
• use the actual SPICE bind host/port and improve non-GUI fallback
• extend shell mocks/tests for the new validation and SPICE behavior

Verification

• local ad-hoc verification for snapshot validation and SPICE fallback
• remote ad-hoc verification on the Proxmox host for live console/SPICE behavior

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Replace wildcard SPICE binds before generating .vv

When QEMU reports a wildcard bind such as address: *:5900, address: :::5900, or 0.0.0.0:5900 for SPICE listening on all interfaces, this assignment stores that bind address as the client host and prevents the fallback at line 1322 from choosing the LAN/override address. The generated URI and .vv then contain host=*, host=::, or host=0.0.0.0, which are bind addresses rather than connectable client targets, so SPICE launch breaks for all-interface binds; normalize wildcard hosts to PROXMOX_MANAGER_SPICE_ADDR/hostname -I while keeping the parsed port.

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