chore(release): v1.2.0 -- the toolbox surface, and a status block that says what it is not

The version moves 1.1.0 -> 1.2.0 in every place it is written: pyproject, the package
__init__, the smoke test that pins it, the README's wheel-install command (gate-pinned
against the build) and uv.lock -- five sites, plus the new CHANGELOG section. A new,
backward-compatible surface, no removals: fourteen run-path steps that had only ever been
reachable through a path that builds a chat client now each have a command of their own.

The README gains a status block at the top, and half of it is what v1 is NOT: no domain
expert has validated an output, three planned rounds of expert feedback were set aside
rather than passed, five of the eight kinds of feedback the design names have no typed way
back into a run, and the multi-agent debate is exercised in the suite only against scripted
clients. That half is the point -- a reader who installs this should learn the limits from
the first screen, not from a gate they have to run themselves.

Measured on this tree at this commit: suite 2238 passed / 0 failed / 5 skipped / 5 xfailed
(769 s), ruff check and mypy src clean, and both gates re-run after staging and unchanged
(v1 gate exit 1: 0/3 - 0/3 - 3/8 - no report - 3/8 - NOT MEASURED - 1/20; B gate exit 1:
15/17 - 0/2 - 15/15 - 0/3 - 4/5 - NOT MEASURED).

No tag is created here.

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

tests/test_smoke.py

@@ -2,4 +2,4 @@ from portfolio_optimiser import __version__
 
 
 def test_version():
-    assert __version__ == "1.1.0"
+    assert __version__ == "1.2.0"