docs(site): align index, quickstart, datasets, and credits to plain watershed framing

[CooperBigFoot]

docs(site): align index, quickstart, datasets, and credits to plain watershed framing

What changed

• docs/index.md: leads with watershed framing, uses the required HFX plain-language phrase, switches install to uv add pyshed with a pip fallback, and updates navigation blurbs without em dashes.
• docs/quickstart.md: switches install guidance, softens first-open guidance, adds the required repeated-delineation sentence, and explains the already-computed connections workflow.
• docs/guide/datasets.md: describes HFX as a folder of pre-built river-network files, replaces remote-read jargon with plain network-fetch language, and preserves hosted GRIT attribution plus the D8-raster fact.
• docs/credits.md: keeps Heberger credit, citations, BibTeX, and lineage while removing outdated how-it-works wording, em dashes, and contrastive-negation phrasing.

Why

These hydrologist-facing pages need to echo the rewritten how-it-works.md
framing: shed returns a watershed by looking up already-computed catchment
connections and merging the upstream units. The edits also apply the campaign
style rules for simpler language, install guidance, no performance numbers, and
no unexplained engineering jargon.

Verification

1. /Users/nicolaslazaro/Desktop/work/shed/crates/python/.venv/bin/mkdocs build --strict -f mkdocs.yml -d .mkdocs-site-check && rm -rf .mkdocs-site-check: passed.
2. ! grep -n '—' docs/index.md docs/quickstart.md docs/guide/datasets.md docs/credits.md: passed.
3. ! grep -nwiE 'minute|minutes|second|seconds|millisecond|milliseconds|ms' docs/index.md docs/quickstart.md docs/guide/datasets.md docs/credits.md: passed.
4. ! cat docs/index.md docs/quickstart.md docs/guide/datasets.md docs/credits.md | tr -s '[:space:]' ' ' | grep -oiE 'row.group|range.read|object.store|rayon|pyo3|projjson|hilbert|xdg|arrow|HDX': passed.
5. ! cat docs/index.md docs/quickstart.md docs/guide/datasets.md docs/credits.md | tr -s '[:space:]' ' ' | grep -oiE "does not delineate|does not extend or improve|not a license obligation|n't just|it's not|isn't": passed.
6. ! grep -qi 'hybrid' docs/index.md && ! cat docs/index.md docs/quickstart.md docs/guide/datasets.md docs/credits.md | tr -s '[:space:]' ' ' | grep -oiE 'drainage.basin': passed.
7. ! cat docs/index.md docs/quickstart.md docs/guide/datasets.md docs/credits.md | tr -s '[:space:]' ' ' | grep -oiE 'TerminalRefinementStrategy|bring.your.own|carve': passed.
8. tr -s '[:space:]' ' ' < docs/index.md | grep -q 'uv add pyshed' && tr -s '[:space:]' ' ' < docs/index.md | grep -q 'pip install pyshed' && tr -s '[:space:]' ' ' < docs/quickstart.md | grep -q 'uv add pyshed' && tr -s '[:space:]' ' ' < docs/quickstart.md | grep -q 'pip install pyshed': passed.
9. tr -s '[:space:]' ' ' < docs/index.md | grep -qF 'whole upstream area that drains to it, the watershed' && tr -s '[:space:]' ' ' < docs/index.md | grep -qF 'folder of pre-built river-network files' && tr -s '[:space:]' ' ' < docs/guide/datasets.md | grep -qF 'folder of pre-built river-network files' && tr -s '[:space:]' ' ' < docs/quickstart.md | grep -qF 'reuse data already fetched, so overlapping watersheds are faster' && grep -qi 'connections' docs/quickstart.md: passed.
10. grep -qi 'slower' docs/quickstart.md && grep -qi 'reuse' docs/quickstart.md && grep -qi 'slower' docs/guide/datasets.md && grep -qi 'reuse' docs/guide/datasets.md: passed.
11. grep -q 'Heberger' docs/credits.md && grep -q '0000-0001-9122-0030' docs/credits.md && grep -q 'github.com/mheberger/delineator' docs/credits.md && grep -q 'doi.org/10.2139/ssrn.5939056' docs/credits.md && grep -q '@software{delineator' docs/credits.md && grep -q 'Djokic' docs/credits.md && grep -q 'mghydro.com/watersheds' docs/credits.md: passed.
12. tr -s '[:space:]' ' ' < docs/guide/datasets.md | grep -qF 'Upstream Tech' && grep -q 'flow_dir.tif' docs/guide/datasets.md && tr -s '[:space:]' ' ' < docs/guide/datasets.md | grep -qi 'no D8 raster': passed.
13. git show --name-only --format= HEAD | sort: passed with exactly docs/credits.md, docs/guide/datasets.md, docs/index.md, and docs/quickstart.md.