chore(make): hide nextest and cargo progress bars in gate targets

[panghy]

Why

Agents run the Rust gates as saved command-mode ws.script entries, which are PTY-backed. nextest and cargo therefore see an interactive stderr and redraw their progress bars into the captured buffer. One full intent-acp + intent-services run produced ~530 KB of ESC[10A / ESC[2K / ESC[1B cursor-control sequences around a few useful lines; the hook wake built from that buffer overflowed an agent's context (413) and cost a re-delegation.

make test-intentd already pipes nextest's stdout through scripts/resumable_nextest.py, so the noise is entirely on stderr (nextest progress bar + cargo build progress) — environment variables fix both without touching the Python wrapper.

What

• Makefile: target-specific export NEXTEST_SHOW_PROGRESS ?= none on gate test test-intentd coverage-e2e coverage-all and export CARGO_TERM_PROGRESS_WHEN ?= never on those plus check clippy build-intentd. ?= keeps env / command-line overrides working (make test NEXTEST_SHOW_PROGRESS=bar restores the bar for a human at a terminal). NEXTEST_HIDE_PROGRESS_BAR is deprecated on the pinned nextest 0.9.143, hence NEXTEST_SHOW_PROGRESS.
• AGENTS.md (Resuming local Rust gates): compress the saved-script bullet to name the PTY hazard and the two flags, pointing at the make targets.

CI already sets CI=true, under which both tools are non-interactive; CI output is unchanged.

Companion docs PR on intentd: intent-hq/intentd — "docs(agents): lead the Gates section with make targets and the PTY progress-bar caveat" (link in the PR conversation once opened).

Verification

• make -n gate test coverage-all check parse; make -p shows the target-specific bindings; make -n test-intentd NEXTEST_SHOW_PROGRESS=bar reports the command-line value winning.
• make test-intentd as a PTY-backed saved script: cursor-sequence count in ws.script.output is 0 (evidence in the workspace spec).
• make docs-check passes.

[panghy]

Companion intentd docs PR: intent-hq/intentd#1795

[augmentcode]

🤖 Augment PR Summary

Summary: This PR suppresses interactive Cargo and nextest progress rendering for Make-based Rust gates run through PTY-backed saved scripts.

Changes: It adds overrideable target-scoped environment defaults in the Makefile and documents the PTY output-buffer hazard and equivalent raw-command flags in AGENTS.md.

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