Switch broken CBM example in README to MIS (#1064)

* Fix CBM example in README; align CBM wire format with schema

The README's `pred create CBM ... | pred solve` example was broken on two
fronts: the bound flag is `--bound-k` (not `--bound`), and the schema-driven
factory rejected the generated JSON because `ConsecutiveBlockMinimization`'s
deserialization required `num_rows`/`num_cols` fields that aren't part of
its declared schema (only `matrix` and `bound` are).

Drop the derived dimensions from the wire format entirely via
`serde(into = ConsecutiveBlockMinimizationDef)` so serialize and deserialize
both use the minimal `{matrix, bound}` form that matches `ProblemSchemaEntry`.
Replace the now-irrelevant inconsistent-dimensions test with one that pins
the minimal wire format and one that exercises ragged-matrix rejection.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* Switch README example to MIS; revert CBM source changes

The previous commit on this branch fixed a CBM serde inconsistency to make
the original `pred create CBM ... --bound-k 2` example run end-to-end. Use
MaximumIndependentSet instead — it works against `main` as-is, and a small
4-vertex path-graph example is more recognizable to readers than CBM's
2x3 boolean matrix. This reverts the CBM model + test changes so this PR
is purely a README fix; the CBM serde alignment can land separately.

Verified: `pred create MIS --graph 0-1,1-2,2-3 --weights 1,1,1,1 |
pred solve - --solver brute-force` returns Max(2) with witness [0,1,0,1].

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: GiggleLiu

README.md

@@ -32,11 +32,11 @@ make cli    # builds target/release/pred
 Try it out:
 
 ```bash
-# Show the Consecutive Block Minimization model (alias: CBM)
-pred show CBM
+# Show the Maximum Independent Set model (alias: MIS)
+pred show MIS
 
-# Create and solve a small CBM instance
-pred create CBM --matrix '[[true,false,true],[false,true,true]]' --bound 2 \
+# Create and solve MIS on the path graph 0-1-2-3
+pred create MIS --graph 0-1,1-2,2-3 --weights 1,1,1,1 \
   | pred solve - --solver brute-force
 ```