refactor(ctl): add structured fetch helpers as MCP groundwork

[neiljar]

What type of PR is this?

/kind enhancement

What this PR does / why we need it:

Groundwork for the Kmesh MCP server (#1800). Today many kmeshctl commands print tables and call os.Exit on failure. An MCP process reusing that code would get unstructured text or crash.

This PR extracts typed fetch helpers that return data + error, wires CLI through RunE, and adds unit tests for HTTP helpers. It does not add the mcp/ server.

Changes:

• version / log / dump / authz — Fetch* / Get* helpers; RunE; no library os.Exit; Writer-based CLI output
• waypoint — ListWaypoints, GetWaypointStatuses (no wait); list command uses them
• health (new) — FetchDaemonHealth / GetDaemonHealth for /debug/ready
• utils — ListDaemonPods, ListMeshNamespaces
• monitoring / secret — same error/RunE cleanup
• tests — httptest coverage for version, log, dump, authz, health fetch paths

Which issue(s) this PR fixes:
Related to #1800

Special notes for your reviewer:

• Prefer merging the status-server PR first (mode on /version, GET /authz). Authz fetch expects GET /authz → {"enabled": bool}feat(status): expose mode on /version and GET /authz #1899
• Complementary to refactor(ctl): decouple kmeshctl output from os.Stdout for MCP integration #1831 (Writer swap); this adds structured returns + error handling.

Does this PR introduce a user-facing change?:

NONE

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