docs: README refresh follow-ups - honest install docs and Alpha classifiers

[mikemcdougall]

Fixes #181

Summary

Doc-side follow-ups from the README refresh (#180). Recon against current trunk confirmed both doc items were still stale; the PyPI publish itself remains an operator action (verified pypi.org still returns 404 for honua-sdk and honua-admin).

Changes Made

• INSTALL.md: replaced the bare pip install honua-sdk / pip install honua-admin section with the from-source clone install and git-URL install, matching the README, with a clear "not yet published to PyPI" statement and a note that the commands collapse to plain pip install after first publish.
• README.md: dropped the now-obsolete caveat that INSTALL.md's pip install honua-sdk commands "apply once the packages are published" (INSTALL.md no longer shows them as the current path).
• packages/honua-sdk/pyproject.toml, packages/honua-admin/pyproject.toml: downgraded Development Status :: 5 - Production/Stable to Development Status :: 3 - Alpha, matching the documented alpha 0.x status. (honua-gp was already 3 - Alpha; honua-arcpy is 7 - Inactive.)

Verification

• Both pyprojects parse (tomllib).
• Touched files are outside the mkdocs docs_dir, so the strict docs build is unaffected; no build/test matrix run for this doc-only change.

Operator items remaining (not addressed here)

• First publish of honua-sdk / honua-admin to PyPI via the Trusted Publishing workflow — tracked separately in Complete PyPI trusted publishing for honua-sdk and honua-admin #178; docs intentionally continue to state that the packages are not yet on PyPI.

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[mikemcdougall]

Lint triage: the lint failure was unrelated to this PR — CI installs unpinned ruff (pip install ruff), and a new ruff release promoted PLR0917 (too many positional arguments), firing on trunk's _elevation_profile_params in packages/honua-sdk/honua_sdk/protocols/scenes.py. Fixed here by making the helper's params keyword-only and updating both call sites; ruff check . (latest) passes repo-wide and tests/test_scenes.py passes 38/38. Consider pinning the ruff version in ci.yml as a follow-up so lint can't break on ruff releases. The staging-smoke failure is also unrelated: trunk's staging integration has been failing with the same 403/test_service errors since 2026-07-25 (pre-existing staging-environment state).