fix(mp2): aligned tables and ASCII boxes are layout, not context stuffing

[Mark2Mac]

The problem

MP2 (context window stuffing) matches (.{2,20}?)\1{20,} — a short unit repeated twenty times or more. There is already a guard for the obvious false positive:

non_ws_chars = set(captured) - {" ", "\t", "\n", "\r"}
if len(non_ws_chars) <= 1 and not any(c in captured for c in (" ", "\t")):
    continue

A run of one repeated character is skipped — but whitespace is explicitly exempted from that skip, so any unit containing a space still matches. In practice that is most formatting a real project contains:

| campo      | quando              | significato                       |
| ---------- | ------------------- | --------------------------------- |

│  └───────────────────────────────────────────────────────┘  │

lines.append(f"{Colors.DIM}│{Colors.RESET}                                   ")

An aligned table, an ASCII box, a padded column. None of them displaces anything.

The change

The existing guard's reasoning, extended to the case it misses: a unit made only of whitespace and alignment characters — dashes, bars, colons, dots, box drawing U+2500–U+257F — repeats because something is being lined up.

It is deliberately not a blanket exemption. Above 400 characters layout stops being a plausible explanation, so a long run is still reported even when it is pure filler:

input	before	after
aligned markdown table	MP2	—
ASCII box / horizontal rule	MP2	—
padded column built in code	MP2	—
"testo" + " " * 800	MP2	MP2
"lorem " * 60 (repeated content)	MP2	MP2

Measured effect

25 real files taken from a corpus of 65 skill/plugin units, every one of which had MP2 findings:

MP2 findings   95  ->  3

The three survivors come from MP2's other patterns — prose that talks about exceeding the context window — not from the repetition pattern. They are a different question and this PR does not touch them.

Tests

Five new cases alongside the existing test_mp2_separator_not_flagged: aligned table, ASCII box and padded column produce nothing; a whitespace run past the layout width, and repeated content, still do.

Full suite: 1565 passed, 14 skipped, 6 xfailed.

[rng1995]

[Automated SkillSpector Review]

Approved. The MP2 exemption is narrowly limited to short runs made only of whitespace/alignment characters; repeated content and long whitespace stuffing remain detected. The new table, box, padded-column, long-run, and repeated-content cases cover both sides of the boundary, and the focused pattern suite passes (244 tests).