fix(dimensions): diameter and radius callouts measured the leader as geometry

`add_diameter_dim` / `add_radius_dim` measure to the point they are handed;
`leader_length` is a text placement. The ezdxf backend passed
`centre + (radius + leader)` as that point, so the leader became part of the
measurement: a true 40 mm bore was dimensioned 60 at the default
`leader_length=10`, and 108 at 34. Radius callouts were `leader_length` too
large the same way.

This is the worst class of defect for this project -- a wrong number, at
default settings, on the one part of a drawing that exists to carry numbers --
and it shipped in v1.4.0 and earlier. The size now comes from `radius` and
`location` only places the text.

The live COM backend was never affected: ActiveX's AddDimDiametric takes the
two chord points and the leader length as separate arguments. The two engines
had been disagreeing by 2 x leader_length on the same call.

Found while building the drawing for the new README, whose own bore callout was
wrong. Two checks added to correctness_suite.py; both report fail -> pass
against v1.4.0, not miss -> pass, which is what separates a repaired defect
from new capability in that lane. A/B is now 21/26 -> 26/26, five fixed, zero
regressed.

README rewritten from scratch
- Hero is a real ISO A3 sheet the server drew: m6 z24 involute spur gear, DIN
  6885 keyed bore, section A-A, ISO 129 dimensions, ISO 286 H7 fit, ISO 7200
  title block, 56 entities, drawing_critique clean. New
  scripts/render_readme_showcase.py rebuilds it, and the tool-call sequence
  that produces it is printed in the page.
- Star history chart, badge row, capability matrix, five evidence lanes, and a
  "what this release is bad at" section carrying the 28% throughput regression.
- Every image and repo link is now an absolute URL: README.md is the PyPI long
  description, where relative paths 404.

Corrections this work forced, all measured
- The df=0 example was wrong. FILLET is already in entity_fillet's own text;
  the commands that genuinely scored zero are WBLOCK, PEDIT, OVERKILL,
  LAYTRANS and MATCHPROP.
- 40,305 tokens is the tools/list wire payload; ~25,143 is the part forwarded
  to the model. The old wording said "of schema", which is neither.
- `--tokenizer anthropic` needs a package and credentials this repo does not
  lock, and refuses rather than falling back. Said so.
- Discovery ranks over the 149-tool advertised catalog, not the 154 registered.
- Five middlewares, not four; the fifth is what makes refusals machine-readable.
- Five of the 27 capability keys are environment-dependent, so the matrix
  carries footnotes instead of bare ticks.
- "Every coordinate is WCS" has one deliberate exception: TEXT rotation.
- render_live_chart's axis still said "fixed 10-task matrix" while our bar came
  from v3's fifteen. Each bar now carries its own matrix.
- .env.example said MAX_UNDO_STACK=50 (code: 5) and omitted four real
  variables, two of them the remote-HTTP controls.
- server.json described an empty ALLOWED_PATHS as blocking access. It disables
  the allowlist.
- server.py called the lean profile ~46 tools; it is 47.
- backends/capability.py cited a test file that does not exist.

1249 passed, 1 xfailed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

benchmarks/render_live_chart.py

@@ -51,6 +51,12 @@ def render_chart(reports: list[dict[str, Any]], output: Path) -> None:
     coverage = [item["summary"]["coverage_percent"] for item in reports]
     passed = [item["summary"]["passed"] for item in reports]
     attempted = [item["summary"]["attempted"] for item in reports]
+    # Which task set each server actually ran. Not decoration: since v1.5.0
+    # the reference adapter runs the 15-task v3 matrix while the pinned
+    # competitor reports are v2 runs from v1.4, so the bars do not share a
+    # denominator and a chart that implies they do is the lie this lane
+    # exists to avoid.
+    matrices = [item.get("matrix", "v2") for item in reports]
     colors = ["#58a6ff" if label == "autocad-mcp-pro" else "#484f58" for label in labels]
 
     fig, ax = plt.subplots(figsize=(12, 4.8), constrained_layout=True)
@@ -60,7 +66,9 @@ def render_chart(reports: list[dict[str, Any]], output: Path) -> None:
 
     ax.set_xlim(0, 100)
     ax.set_xlabel(
-        "Weighted live-run score / 100 (fixed 10-task matrix)", color="#e6edf3", labelpad=10
+        "Weighted live-run score / 100, within each server's own task matrix",
+        color="#e6edf3",
+        labelpad=10,
     )
     ax.set_title(
         "Live-run benchmark - headless ezdxf lane",
@@ -73,17 +81,20 @@ def render_chart(reports: list[dict[str, Any]], output: Path) -> None:
     ax.text(
         0,
         1.02,
-        "Same 10 tasks, same harness, pinned competitor commits; artifacts verified by re-opening the DXF",
+        "Same harness, pinned competitor commits; artifacts verified by re-opening the DXF. "
+        "Matrices differ - read the per-bar label.",
         transform=ax.transAxes,
         color="#8b949e",
         fontsize=10,
     )
 
-    for bar, score, cov, ok, total in zip(bars, scores, coverage, passed, attempted, strict=True):
+    for bar, score, cov, ok, total, matrix in zip(
+        bars, scores, coverage, passed, attempted, matrices, strict=True
+    ):
         ax.text(
-            min(score + 1.2, 82),
+            min(score + 1.2, 76),
             bar.get_y() + bar.get_height() / 2,
-            f"{score:g}  ({ok}/{total} pass, {cov:g}% coverage)",
+            f"{score:g}  ({ok}/{total} pass, {cov:g}% coverage, matrix {matrix})",
             va="center",
             color="#e6edf3",
             fontweight="bold",
@@ -92,7 +103,9 @@ def render_chart(reports: list[dict[str, Any]], output: Path) -> None:
     ax.text(
         0,
         -0.22,
-        "Unsupported tasks score 0 in the fixed matrix; per-task statuses and reasons are in benchmarks/results/published/.",
+        "Unsupported tasks score 0 within a server's own matrix. The five v3 tasks were "
+        "added after the competitor runs and were never put to them; per-task statuses are "
+        "in benchmarks/results/published/.",
         transform=ax.transAxes,
         color="#8b949e",
         fontsize=9,