Regression tests from PR #51586: the inspection agent must receive the
platform-resolved enabled_toolsets and agent.disabled_toolsets, and a
Blank Slate profile's prompt-size must count exactly the 6 file/terminal
tool schemas.
Adds a 'hermes prompt-size' command that reports the fixed prompt budget
for a fresh session: system prompt total, skills index, memory, user
profile, prompt tiers, and tool-schema JSON bytes. Runs offline (dummy
credentials force the direct-construction path, no network call).
Lets users see which block dominates their per-call payload — the skills
index is often the largest single block when many skills are installed
(issue #34667). Zero model-tool footprint: it's a top-level CLI
subcommand, not an agent tool.
--platform <name> simulates a channel's platform hint; --json emits a
machine-readable breakdown.
Closes#34667
