docs: show that da-cli is on PyPI

[FZ2000]

Problem

The install instructions have been correct since #7, and #11 fixed what PyPI
says about the project. This fixes what the project says about PyPI.

Nothing above the fold indicated the package was installable. The badge row —
eight badges covering CI, Python, licence, ruff, mypy, coverage, status and
dependency count — never mentioned PyPI, so a visitor's first screen gave no
sign that pipx install da-sync existed. (The name does appear further down,
in the Install section; the gap was at the top.)

Solution

• PyPI version badge, first in the row, linking to the project page.
• pipx install da-sync directly under the opening paragraph.
• Python 3.10+ → pypi/pyversions, which reads the classifiers instead
  of restating them, so it cannot drift from requires-python. It renders
  3.10 | 3.11 | 3.12 | 3.13 | 3.14 — strictly more than the static badge.
• Dropped Status: Beta. The blockquote two lines below already says it
  with more detail.

That last one was forced, and the reason is worth recording: the badge row has
a budget. check_discoverability requires deviantart within the first twelve
source lines, and a ninth badge pushed the opening paragraph past it. Trimming
the duplicate beat widening the rule — that would have traded a real SEO
constraint for badge clutter.

Verification

• All three new badge URLs were fetched and render real data — pypi: v0.1.1 and python: 3.10 | 3.11 | 3.12 | 3.13 | 3.14 — not shields'
  invalid/undefined placeholder, which is what a wrong package name yields.
• The opening-lines rule was watched failing: inserting a filler ninth
  badge reproduced FAIL 'deviantart' appears in the H1 or opening lines,
  27 passed / 1 failed. Restored, it is 28 passed / 0 failed.
• check_doc_flags, check_doc_references, check_version_sync,
  check_discoverability — all pass.
• markdownlint (pinned 0.45.0 + repo config) clean; lychee 0 errors.

Note

The badge will not appear on the PyPI page until the next release, since a
description is frozen into the uploaded artifact. That is cosmetic and not
worth a release on its own — 0.1.1's description is already correct.

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