PDFCLOUD-5597 Readme updates

[datalogics-kam]

PDFCLOUD-5597

Why this change

The repository README was accurate but too sparse for a public-facing GitHub and
PyPI landing page. It leaned heavily toward maintainer workflow commands and did
not reflect the SDK's current positioning, supported Python versions, or the
ways users discover and evaluate the product (for example API Lab, docs, and
PyPI metadata).

This change improves first-impression quality and onboarding by making the README
more product-forward, easier to scan, and more useful for both developers and
LLM-assisted tooling. It also moves contributor-focused commands out of the main
README so end users see a cleaner install + quickstart path.

What changed (high level)

This PR refreshes documentation and packaging metadata without changing runtime
SDK behavior.

• Rewrote README.md as a user-facing landing page with stronger product
  positioning, capabilities overview, AI/LLM workflow framing, and sync/async
  quickstarts.
• Made install guidance uv-first while keeping pip as a clear fallback for
  PyPI users.
• Added top-of-README badges for CI status, PyPI version, supported Python
  versions, and llms.txt availability.
• Moved contributor/dev workflow commands into a new CONTRIBUTING.md to keep
  the README focused on product discovery and onboarding.
• Added docs/llms.txt and docs/llms-full.txt to provide machine-readable
  docs indexes/guides for LLM and agent tooling.
• Bumped package version metadata from 1.0.1 to 1.0.2 and synced uv.lock.

Behavior changes

There are no SDK runtime/API behavior changes in this PR.

What is different:

• GitHub and PyPI users will see a substantially improved README experience
  (badges, clearer value proposition, modern install commands, and quickstarts).
• The documentation site will publish llms.txt and llms-full.txt (assuming
  standard MkDocs file passthrough from docs/), which makes the docs easier to
  consume for LLM-based assistants and indexing tools.
• Contributor instructions now live in CONTRIBUTING.md instead of the README.

Validation

Validation performed:

• Reviewed upstream/main..HEAD diff for correctness and scope.
• Verified README claims against current repository/package state, including:
  • supported Python versions (>=3.10 / CI matrix 3.10-3.14)
  • workflow file name used by the CI badge (test-and-publish.yml)
  • docs site URL and docs page paths used in links
  • SDK public client names (PdfRestClient, AsyncPdfRestClient)
• Confirmed PR branch/title alignment with Jira key (PDFCLOUD-5597).

Not run (docs-only/package-metadata PR):

• uv run ruff format .
• uv run ruff check .
• uv run basedpyright
• uv run pytest -n auto --maxschedchunk 2
• uvx nox -s tests
• uv run mkdocs build --strict

Risks and follow-ups

Primary risks are documentation quality/deployment concerns rather than code
regressions:

• README links/badges depend on canonical upstream repo/docs URLs remaining
  stable.
• llms.txt and llms-full.txt badges/links assume the docs deployment serves
  raw files from the MkDocs docs/ directory at the site root.
• Version bump to 1.0.2 should align with release intent/timing for this PR.

Follow-ups (if desired):

• Add a docs build check run for this branch before merge to verify llms.txt
  and llms-full.txt publish at the expected paths.
• Consider linking llms-full.txt from the docs home page in addition to the
  machine-readable llms.txt path.

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