chore(release): 1.0.0b1 — the v1 target, staged as a beta

All seven v1 capabilities are landed (ROADMAP's v1 target is met), so this is
the first release of the 1.x train. Staged as a beta rather than cut final on
the operator's call: per the canonical policy `-beta.N` means feature-complete,
external testing, no new features, focus is on bugs — which is exactly this
state, with a cross-frontier bug-hunt panel outstanding on U7's diff.

The repo learned this sequencing the hard way once: v0.2.0 was tagged and
announced while a contract panel was in flight, the panel found three defects in
the code just released, and v0.2.1 shipped within the hour. A beta is the
designed answer to that, not a workaround for it.

ALSO FIXES A SECOND COPY OF THE VERSION, found while cutting this one.
`booth.__version__` was the literal `0.1.0` and had been wrong through six
releases. It is now read from pyproject.toml — deliberately NOT from
importlib.metadata, which describes a different artifact: this repo has no build
step and no install step (booth.service runs uvicorn with WorkingDirectory set
to the tree), and the venv was carrying a vestigial booth-0.3.0.dist-info with
no package directory behind it. Installed metadata therefore reported 0.3.0 for
a tree at 1.0.0b1 — confidently wrong and varying by environment, which is worse
than a literal that at least fails the same way everywhere.

booth/__init__.py is also, it turns out, effectively stdlib-only: scripts/booth
imports booth.links / booth.marks / booth.manifest under the system python3 with
no venv, and every one of those executes the package root first. Nothing
asserted it. test_stdlib_only now covers __init__, and the no-venv import path
is verified under python3.11 reporting 1.0.0b1.

642 tests green.

ROADMAP.md

@@ -1,9 +1,12 @@
 # The Booth — roadmap
 
 Design: [`docs/design/information-architecture.md`](docs/design/information-architecture.md).
-Current version: `0.6.1` (**U1 through U7 landed — every v1 capability is in**;
-extracted from eshpfi 2026-09-21). **The 1.0 cut is now a decision, not a
-dependency**, and it is the operator's: a major bump needs his approval.
+Current version: `1.0.0b1` (**U1 through U7 landed — every v1 capability is
+in**; extracted from eshpfi 2026-09-21). **The v1 target is MET and staged as a
+beta** (operator, 2026-09-22): feature-complete, external testing, no new
+features — the remaining work is bugs. `1.0.0` final is cut when the beta
+survives; per the canonical policy an rc would be cut from the same commit,
+but a beta may still take fixes.
 
 ## v1 target