Fix the budget gate and add CI, lint and coverage guards

- check_budget.py escalated a hard index-row violation to 'warn' on both
  branches, so INDEX_ROW_HARD could never fail anything. It fails now, and
  tests/unit/test_budget_measurement.py pins both thresholds.
- The corpus note counted scripts/__pycache__/*.pyc, so the same commit
  reported 27 scripts after the suite had run and 16 on a clean checkout.
- TOKENS_PER_CHAR is re-derived from a measurement (26,795 chars -> 6,065
  tokens = 4.418); the comment's old figure and its arithmetic were both
  wrong for this file.
- check_repo.py's yaml sentinel carries the type ignore, so mypy is clean
  with PyYAML installed as well as without it.
- The CPUID test now skips with the probe's own note on a host without
  CPUID instead of failing, and pytest.ini points at tests/README.md, which
  exists, instead of an EXTENSION file that never did.

Tooling: .flake8 (a measured 120-column limit), .gitattributes, .gitignore
and .github/workflows/ci.yml (the five gates, the suite on 3.11-3.14 and a
lint job), which is what CONTRIBUTING.md already claimed CI runs. The
pull-request template it refers to now exists.

Content: pitfalls P26-P34 -- the analysis-level failures the catalogue was
missing (sampling read as observation, a self-built parser trusted, a
verification that could not have failed, a shell-mangled command line) --
registered in the symptom index and its routing mirror. FINDINGS F11-F15
record the defects above.

Tests: the coverage guard derives its subject from scripts/ rather than a
hand-written list, pe_triage.py and pe_diff.py gain their first tests, and
plan.py / preflight.py are declared uncovered with reasons.

tests/cli/test_cli_coverage.py

@@ -0,0 +1,80 @@
+"""Coverage of the shipped scripts, derived from the directory rather than a hand-written list.
+
+Borrowed mechanism: the sibling apk-reverse repository derives its CLI contract cases from
+skills/*/scripts/*.py and from each script's own --help output, so a new script is covered the day
+it lands instead of the day someone remembers to add it. What is *not* borrowed is that repository's
+single 0-4 exit-code table: this kit publishes a per-script vocabulary (pepatch.py uses 3 for "not a
+parseable PE", where the table means "the environment lacks a capability"), and a test that rewrote
+those meanings would assert a policy this repository deliberately does not have.
+
+The guard here is therefore narrower, and it is about *coverage*, not exit codes:
+
+  * every shipped .py is either in conftest.SCRIPT_FILES (some layer of this suite exercises it) or
+    named in DECLARED_UNCOVERED together with the reason it is not;
+  * every declared gap carries a real sentence, because "TODO" is how a gap becomes permanent;
+  * every shipped script -- covered or declared -- answers --help with its usage block, which is the
+    cheapest possible exercise of its argparse table and its import path.
+
+A new script fails this file until one of those lists changes. That is the point: the alternative
+is a suite that looks complete while silently ignoring half the kit.
+"""
+import subprocess
+import sys
+
+import pytest
+
+from conftest import SCRIPTS_DIR, SCRIPT_FILES
+
+pytestmark = pytest.mark.cli
+
+# Scripts no layer exercises yet. Each entry is a recorded gap, not an exemption: the reason says
+# what would be needed to close it, so the next pass can decide rather than rediscover.
+DECLARED_UNCOVERED = {
+    "plan.py":
+        "composes capabilities.py and doctor.py into a route from a stated intent. Both halves have "
+        "their own tests; the composition reads live host facts, so a fixture that pinned its output "
+        "would pin this machine's capability set instead of the mapping. Closing it needs a stubbed "
+        "probe, and that stub does not exist yet.",
+    "preflight.py":
+        "answers session readiness from live host facts (free space, route prerequisites) plus one "
+        "sample. The sample half could be pinned to a generated PE; the host half has no generator, "
+        "and asserting on the runner's environment would encode this machine as an expectation.",
+}
+
+
+def shipped_scripts():
+    """Every runnable python script the skill ships, sorted."""
+    return sorted(p.name for p in SCRIPTS_DIR.glob("*.py"))
+
+
+def test_every_shipped_script_is_exercised_or_declared():
+    """A script nobody tests must at least be a script somebody decided not to test."""
+    shipped = set(shipped_scripts())
+    assert shipped, "no scripts found under %s" % SCRIPTS_DIR
+    silently_uncovered = shipped - set(SCRIPT_FILES) - set(DECLARED_UNCOVERED)
+    assert not silently_uncovered, (
+        "these scripts are shipped but neither exercised nor declared uncovered: %s. Add a test and "
+        "register the script in conftest.SCRIPT_FILES, or add it to DECLARED_UNCOVERED with the "
+        "reason." % sorted(silently_uncovered))
+
+
+def test_declared_entries_are_neither_stale_nor_hollow():
+    """A gap that was closed must leave the list; a gap with no reason is a hidden one."""
+    both = set(SCRIPT_FILES) & set(DECLARED_UNCOVERED)
+    assert not both, ("these scripts are in SCRIPT_FILES and also declared uncovered: %s -- the "
+                      "declaration is stale" % sorted(both))
+    for name, reason in DECLARED_UNCOVERED.items():
+        assert (SCRIPTS_DIR / name).is_file(), "%s is declared uncovered but does not exist" % name
+        assert len(reason.split()) >= 12, (
+            "%s: the reason must say what would close the gap, not just mark it" % name)
+
+
+@pytest.mark.parametrize("script", shipped_scripts())
+def test_every_shipped_script_answers_help_with_usage(script):
+    """The usage block is the script's published contract; it must render on every host."""
+    proc = subprocess.run([sys.executable, str(SCRIPTS_DIR / script), "--help"],
+                          capture_output=True, text=True, timeout=120,
+                          encoding="utf-8", errors="replace")
+    assert proc.returncode == 0, "%s --help exited %d: %s" % (script, proc.returncode, proc.stderr)
+    assert "usage:" in proc.stdout.lower(), "%s printed no usage block" % script
+    assert script in proc.stdout, "%s does not name itself in its usage line" % script