feat(orbit): rename --format flag to --response-format

What does this MR do and why?

Renames the Orbit --format/-f flag to --response-format (no short flag) on glab orbit remote query and glab orbit remote graph-status, resolving the flag collision raised in !3178 (merged).

--format/-f is a server-side response_format pass-through (llm | raw), but its short flag -f differs from glab's established -F/--output only by case, and the long name overlaps conceptually with client-side output rendering. --response-format mirrors the API field name exactly and signals that it controls what the server returns, not how the CLI renders it. variable export already deprecated its own --format in favour of --output, so this keeps new commands consistent with that direction.

The old --format/-f is kept as a deprecated, hidden alias for one release (graceful migration for CLI scripts), and MarkFlagsMutuallyExclusive turns passing both flags into a clean error rather than silent last-wins. Since both commands are EXPERIMENTAL, this is a cheap clean-up now.

Note on MCP: the deprecation shim does not give MCP agents a discoverability grace period - the advertised tool schema property flips format -> response_format in this release (hidden flags are skipped by schema generation), though stale format calls still execute via the handler's flag lookup.

Closes #8298 (closed)

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