fix(fast-mode): gate seed close on clean lint + passed tests; tester fails on collection errors

[ryanholtschneider2]

What & why

Fixes po-formulas-software-dev-7fl. Two independent gates let 6 real test regressions slip through 7 agent-step gates during the pd-17lv CDR-A epic series.

Root cause

1. software_dev_fast auto-closed the seed regardless of verdict — including when a verdict was empty (the lint/test step never wrote a verdict file, i.e. didn't run / unknown). It only logged a warning, never gated the close.
2. The tester treated pytest collection errors (a module failing to import) as silent skips — it reported passed off the tests that ran while 9 modules dropped on ModuleNotFoundError.

Fix

• Fast-mode close (parent/po_formulas/software_dev.py): close the seed only when lint == "clean" AND unit == "passed". Anything else — empty, non-clean, or non-passed — leaves the seed open and returns status="needs-review" so the caller can re-dispatch or escalate to software-dev-full. This makes the code match the flow's own docstring.
• Tester contract (parent/po_formulas/agents/tester/task.md): run pytest --collect-only first, report a collection_errors count, and treat collection_errors >= 1 as a hard FAILED even if every collected test passed.
• README updated to document the tighter close gate + collection-error rule.

Tests

New parent/tests/test_software_dev_fast.py:

• empty lint verdict → seed NOT closed, status == needs-review (the exact incident)
• failed unit verdict (how a collection error now surfaces) → seed NOT closed
• empty unit verdict → seed NOT closed
• clean + passed → seed closed, status == completed
• tester prompt-contract: --collect-only + collection_errors-gates-on-fail present

Full pack unit suite: green except one pre-existing, order-dependent failure in test_software_dev_pack_path_metadata.py that fails identically on base main in a full-suite run and passes standalone (unrelated to this change).

Acceptance mapping

• ✅ Tester verdict reports collection_errors; ≥1 fails the run.
• ✅ Empty lint_verdict blocks fast-mode auto-close (downgrades to needs-review).
• ✅ Repro: an ImportError surfaces as a FAILED unit verdict → fast-formula does NOT close the seed (covered by test_failed_unit_verdict_blocks_close).