Deletion progress spinner + agent-var classification fix (§4)

[UnbreakableMJ]

Two related UX/conformance improvements to vacuum clean, surfaced while testing the freshly-installed CLI.

1. Deletion progress spinner

Previously, after confirming a real deletion (y, or --apply --yes), run_clean deleted in a loop and printed nothing until the whole loop finished — a multi-GB target/ made the terminal look frozen.

Now vacuum clean --apply shows a live spinner:

⠹ [1/3] Removing /home/you/project/target

• Steady-tick spinner (animates on a background thread) — each candidate is one blocking removal call, so a spinner is the honest signal, not a percent bar that would jump straight to 100%.
• stderr only, so stdout stays data-only (SFRS §7); human/TTY mode only, skipped for --quiet, dry-runs, and JSON/JSONL/agent output; uncolored template satisfies NO_COLOR.
• Implemented with indicatif, contained to vacuum-cli (execute_candidates in app.rs); vacuum-core stays UI-free.

2. Agent-var classification fix (agentic-cli §4)

Testing showed the spinner never appeared under Claude Code because CLAUDECODE was treated as a JSON-forcing agent var. Per agentic-cli §4, CLAUDECODE / CURSOR_AGENT / GEMINI_CLI are informational only.

• Split env vars: forcing = AI_AGENT, AGENT, CI (change output mode / suppress TUI); informational = CLAUDECODE, CURSOR_AGENT, GEMINI_CLI (no behavioral effect).
• Informational agents now surface in metadata.invoking_agent (telemetry only, omitted when absent) — which is what the manual already documented.
• Extracted the pure first_set classifier and added unit tests.

Verification

• Spinner renders under a real-terminal PTY, then clears to the normal summary; piped human-mode keeps stdout free of control chars; invoking_agent:"CLAUDECODE" appears in the envelope while AI_AGENT still correctly forces JSON.
• Gate green: cargo fmt · clippy -D warnings · cargo test --workspace (16 tests) · reuse lint. Commit signed/verified (§6.3).

🤖 Generated with Claude Code